[query] Use SourcePos for implicit timing context

[ehigham]

Change Description

Fixes #<issue_number> (delete if N/A)

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Security Assessment

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Impact Description

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[ehigham]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• [query] Use SourcePos for implicit timing context #14732 👈 (View in Graphite)
• [query] Lowering + Optimisation with implict timing context #14731 : 1 other dependent PR (#14748 )
• [query] Lift backend state into {Service|Py4J}BackendApi #14698
• [query] Move LoweredTableReaderCoercer into ExecuteContext #14696
• [query] unify backend rpc #14693
• [query] Remove persistedIr from Backend interface #14692
• [query] Remove lookupOrCompileCachedFunction from Backend interface #14691
• [query] Remove BlockMatrix persist from Backend interface #14690
• [query] Expose references via ExecuteContext #14686
• [query] Extract Backend Methods called from Python into Py4JBackendExtensions #14767
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