revamp juxtaposed function call parsing

[janw4ld]

hellooo, regarding #5, i got juxtaposed function calls working more robustly by

• adding a new expression kind for those that can be juxtaposed callees
• modifying the precedence of almost everything🫣
• adding a not really valid assumption that all non-builtin type identifiers start with a capital letter. this is only true by convention, but i really think there's no other way for determining if string hello is a declaration or function call before run time

the current issue with this refactor thing is that it parses regular function calls with one argument print("hello") as a juxt function call with one parenthesized argument instead of a regular function call. i'll have another try with it to make sure parenthesized_expression is never the argument of a juxt call but wanted to share the news / have you as a second pair of fresh eyes

[janw4ld]

not very sure what cases this does and doesn't cover, but it passes the parser's tests (except for the issue above), and detects these calls as such (they and others are incorrectly marked as declarations instead of juxt function calls in test snapshots).

[murtaza64]

Really happy that you're working on this! Can't promise that I'll have time to take a look this weekend, but if you get too stuck I might be able to spend some time investigating next week

[janw4ld]

@murtaza64 this works really well now. please note that this PR contains #32's commits too, and a bunch of miscellaneous fixes to uncommon syntax i personally use in my jenkins libraries. i've validated every node in the new test i added and i'm sure it's parsed correctly.