Project symbol index enhancements

[nicklockwood]

This PR extends the work started in #2722 by adding Xcode project file parsing to determine file target membership.

I've also extended the trailingClosures, commonTypos and acronyms rules to use the project index.

[codecov]

Codecov Report

❌ Patch coverage is 96.03699% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.64%. Comparing base (89df751) to head (3b93c83).

Files with missing lines	Patch %	Lines
Sources/ProjectIndex.swift	95.74%	28 Missing ⚠️
Sources/FormattingHelpers.swift	93.54%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2738      +/-   ##
===========================================
+ Coverage    95.62%   95.64%   +0.02%     
===========================================
  Files          191      191              
  Lines        29921    30601     +680     
===========================================
+ Hits         28611    29269     +658     
- Misses        1310     1332      +22     

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