[repo] Build script organization

[CodeBlanch]

Changes

• Moves the remaining build scripts into the .build\scripts\ subfolder.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.78%. Comparing base (6250307) to head (02ad67f).
Report is 225 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5619      +/-   ##
==========================================
+ Coverage   83.38%   85.78%   +2.40%     
==========================================
  Files         297      254      -43     
  Lines       12531    10982    -1549     
==========================================
- Hits        10449     9421    -1028     
+ Misses       2082     1561     -521     

Flag	Coverage Δ
unittests	?
unittests-Solution-Experimental	85.77% <ø> (?)
unittests-Solution-Stable	85.77% <ø> (?)
unittests-Unstable-Core	19.84% <ø> (?)

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see 114 files with indirect coverage changes