Better handling of IPM packages mapped from another namespace

[isc-pbarton]

Resolves #997
This works, but feels far too heavyweight and I'm uncertain of the performance impacts. Saving this work against a draft PR, and will put up a separate PR with a more targeted fix to compare.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 57.31707% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.58%. Comparing base (0290792) to head (77a53f4).

Files with missing lines	Patch %	Lines
cls/SourceControl/Git/PackageManagerContext.cls	59.70%	27 Missing ⚠️
cls/SourceControl/Git/Utils.cls	46.66%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1003      +/-   ##
==========================================
+ Coverage   49.92%   50.58%   +0.65%     
==========================================
  Files          23       23              
  Lines        3373     3446      +73     
==========================================
+ Hits         1684     1743      +59     
- Misses       1689     1703      +14     

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