Allow for initializing a PBXProj via a direct path

[maxwellE]

Short description 📝

Allows for a pbxproj path to be initiated with a direct path, also
moves some related code to the PBXProj class

Solution 📦

Simply moves around the code that already exists and opens some ACLs to allow callers of the library to use this code

Implementation 👩‍💻👨‍💻

N/A

[codecov-commenter]

Codecov Report

Merging #682 (958b01d) into main (92e43ed) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #682      +/-   ##
==========================================
+ Coverage   84.81%   84.84%   +0.03%     
==========================================
  Files         157      157              
  Lines        9026     9044      +18     
==========================================
+ Hits         7655     7673      +18     
  Misses       1371     1371              

Impacted Files	Coverage Δ
Sources/XcodeProj/Objects/Project/PBXProj.swift	78.83% <100.00%> (+7.54%)	⬆️
Sources/XcodeProj/Project/XcodeProj.swift	28.98% <100.00%> (-14.70%)	⬇️

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[fortmarek]

I don't see why not make this reusable but would wait for @kwridan review before merging 👍

[kwridan]

Thank you for submitting this @maxwellE !

I recall needing a public accessor to PBXProj a while back when I prototyped bloomberg/xcdiff#25 😅

[kwridan]

Thanks for the updates @maxwellE