ci: Update Dotty to use Microsoft.Build package for csproj parsing

[tippmar-nr]

A quick update to Dotty that uses the Microsoft.Build package to parse csproj files and manage updates to package versions. We now report the version in the project file as the "old" version and the latest Nuget package version as the "updated to" version.

This work lays the foundation for later work to extract the current set of package versions used in our project files for purposes of building the compatibility documentation.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.19%. Comparing base (d98e2da) to head (e76392b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3079   +/-   ##
=======================================
  Coverage   82.19%   82.19%           
=======================================
  Files         477      477           
  Lines       30627    30627           
  Branches     3426     3426           
=======================================
+ Hits        25173    25175    +2     
+ Misses       4655     4653    -2     
  Partials      799      799           

Flag	Coverage Δ
Agent	83.25% <ø> (+<0.01%)	⬆️
Profiler	72.51% <ø> (ø)

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see 2 files with indirect coverage changes

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