Upgrade to .NET 6 and modernize code

.editorconfig

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+# editorconfig.org
+
+# This file should be kept in sync across https://www.github.com/dotnet/wpf and dotnet-wpf-int repos.
+# top-most EditorConfig file
+root = true
+
+# Default settings:
+# A newline ending every file
+# Use 4 spaces as indentation
+[*]
+trim_trailing_whitespace = true
+insert_final_newline = true
+indent_style = space
+indent_size = 4
+
+[project.json]
+indent_size = 2
+
+# C# files
+[*.cs]
+# New line preferences
+csharp_new_line_before_open_brace = all
+csharp_new_line_before_else = true
+csharp_new_line_before_catch = true
+csharp_new_line_before_finally = true
+csharp_new_line_before_members_in_object_initializers = true
+csharp_new_line_before_members_in_anonymous_types = true
+csharp_new_line_between_query_expression_clauses = true
+
+# Indentation preferences
+csharp_indent_block_contents = true
+csharp_indent_braces = false
+csharp_indent_case_contents = true
+csharp_indent_switch_labels = true
+csharp_indent_labels = one_less_than_current
+
+# avoid this. unless absolutely necessary
+dotnet_style_qualification_for_field = false:suggestion
+dotnet_style_qualification_for_property = false:suggestion
+dotnet_style_qualification_for_method = false:suggestion
+dotnet_style_qualification_for_event = false:suggestion
+
+# only use var when it's obvious what the variable type is
+csharp_style_var_for_built_in_types = false:none
+csharp_style_var_when_type_is_apparent = false:none
+csharp_style_var_elsewhere = false:none
+
+# use language keywords instead of BCL types
+dotnet_style_predefined_type_for_locals_parameters_members = true:suggestion
+dotnet_style_predefined_type_for_member_access = true:suggestion
+
+# name all constant fields using PascalCase
+dotnet_naming_rule.constant_fields_should_be_pascal_case.severity = suggestion
+dotnet_naming_rule.constant_fields_should_be_pascal_case.symbols  = constant_fields
+dotnet_naming_rule.constant_fields_should_be_pascal_case.style    = pascal_case_style
+
+dotnet_naming_symbols.constant_fields.applicable_kinds   = field
+dotnet_naming_symbols.constant_fields.required_modifiers = const
+
+dotnet_naming_style.pascal_case_style.capitalization = pascal_case
+
+# static fields should have s_ prefix
+dotnet_naming_rule.static_fields_should_have_prefix.severity = suggestion
+dotnet_naming_rule.static_fields_should_have_prefix.symbols  = static_fields
+dotnet_naming_rule.static_fields_should_have_prefix.style    = static_prefix_style
+
+dotnet_naming_symbols.static_fields.applicable_kinds   = field
+dotnet_naming_symbols.static_fields.required_modifiers = static
+dotnet_naming_symbols.static_fields.applicable_accessibilities = private, protected, private_protected, local
+
+dotnet_naming_style.static_prefix_style.required_prefix = s_
+dotnet_naming_style.static_prefix_style.capitalization = camel_case
+
+# internal and private fields should be _camelCase
+dotnet_naming_rule.camel_case_for_private_internal_fields.severity = suggestion
+dotnet_naming_rule.camel_case_for_private_internal_fields.symbols  = private_internal_fields
+dotnet_naming_rule.camel_case_for_private_internal_fields.style    = camel_case_underscore_style
+
+dotnet_naming_symbols.private_internal_fields.applicable_kinds = field
+dotnet_naming_symbols.private_internal_fields.applicable_accessibilities = private, internal
+
+dotnet_naming_style.camel_case_underscore_style.required_prefix = _
+dotnet_naming_style.camel_case_underscore_style.capitalization = camel_case
+
+# Code style defaults
+dotnet_sort_system_directives_first = true
+csharp_preserve_single_line_blocks = true
+csharp_preserve_single_line_statements = false
+
+# Expression-level preferences
+dotnet_style_object_initializer = true:suggestion
+dotnet_style_collection_initializer = true:suggestion
+dotnet_style_explicit_tuple_names = true:suggestion
+dotnet_style_coalesce_expression = true:suggestion
+dotnet_style_null_propagation = true:suggestion
+
+# Expression-bodied members
+csharp_style_expression_bodied_methods = false:none
+csharp_style_expression_bodied_constructors = false:none
+csharp_style_expression_bodied_operators = false:none
+csharp_style_expression_bodied_properties = true:none
+csharp_style_expression_bodied_indexers = true:none
+csharp_style_expression_bodied_accessors = true:none
+
+# Pattern matching
+csharp_style_pattern_matching_over_is_with_cast_check = true:suggestion
+csharp_style_pattern_matching_over_as_with_null_check = true:suggestion
+csharp_style_inlined_variable_declaration = true:suggestion
+
+# Null checking preferences
+csharp_style_throw_expression = true:suggestion
+csharp_style_conditional_delegate_call = true:suggestion
+
+# Space preferences
+csharp_space_after_cast = false
+csharp_space_after_colon_in_inheritance_clause = true
+csharp_space_after_comma = true
+csharp_space_after_dot = false
+csharp_space_after_keywords_in_control_flow_statements = true
+csharp_space_after_semicolon_in_for_statement = true
+csharp_space_around_binary_operators = before_and_after
+csharp_space_around_declaration_statements = do_not_ignore
+csharp_space_before_colon_in_inheritance_clause = true
+csharp_space_before_comma = false
+csharp_space_before_dot = false
+csharp_space_before_open_square_brackets = false
+csharp_space_before_semicolon_in_for_statement = false
+csharp_space_between_empty_square_brackets = false
+csharp_space_between_method_call_empty_parameter_list_parentheses = false
+csharp_space_between_method_call_name_and_opening_parenthesis = false
+csharp_space_between_method_call_parameter_list_parentheses = false
+csharp_space_between_method_declaration_empty_parameter_list_parentheses = false
+csharp_space_between_method_declaration_name_and_open_parenthesis = false
+csharp_space_between_method_declaration_parameter_list_parentheses = false
+csharp_space_between_parentheses = false
+csharp_space_between_square_brackets = false
+
+csharp_style_namespace_declarations = file_scoped:suggestion
+
+# Diagnostics
+dotnet_diagnostic.CA1816.severity = none
+dotnet_diagnostic.RCS1156.severity = none
+dotnet_diagnostic.RCS1159.severity = none
+dotnet_diagnostic.RCS1158.severity = none
+dotnet_diagnostic.RCS1154.severity = none
+dotnet_diagnostic.RCS1225.severity = none
+
+# C++ Files
+[*.{cpp,h,in}]
+curly_bracket_next_line = true
+indent_brace_style = Allman
+
+# Visual Studio Solution files
+[*.sln]
+end_of_line = lf
+
+# Xml project files
+[*.{csproj,vcxproj,vcxproj.filters,proj,nativeproj,locproj}]
+indent_size = 2
+
+# Xml build files
+[*.builds]
+indent_size = 2
+
+# Xml files
+[*.{xml,stylecop,resx,ruleset}]
+indent_size = 2
+
+# Xml config files
+[*.{props,targets,config,nuspec}]
+indent_size = 2
+
+# Shell scripts
+[*.sh]
+end_of_line = lf
+[*.{cmd, bat}]
+end_of_line = crlf

Directory.Build.props

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+<Project>
+  <PropertyGroup>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+  <ItemGroup>
+    <Using Include="System.ComponentModel" />
+    <Using Include="System.IO" />
+    <Using Include="System.Windows" />
+    <Using Include="System.Windows.Controls" />
+    <Using Include="System.Windows.Documents" />
+    <Using Include="System.Windows.Input" />
+    <Using Include="System.Windows.Media" />
+    <Using Include="System.Windows.Media.Animation" />
+    <Using Include="System.Windows.Threading" />
+  </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="Roslynator.Analyzers" Version="4.1.1">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+</Project>