Support building on Linux

[paulmedynski]

Work-in Progress

Changes to the build system to support building all targets on Linux. This mostly involved removing properties from build.proj that artifically restricted what would be built based on the OS, and then filtering those changes down into all of the project files.

Major Changes:

• All projects can be built on Windows and Linux.
  • macOS has not been fully tested due to a lack of hardware, but CI builds on macOS are working.
• The TF property is now used to explicitly decide what Target Frameworks to specify when building AKV and tests, and running tests.
  • This replaces many build.proj properties:
    • IsEnabledWindows
    • TargetGroup
    • TargetNetFxVersion
    • TargetNetCoreVersion
    • TestOS
    • TestTargetOS
    • TFGroup
  • If you don't specify TF then all Target Frameworks are built (net462, net8.0, net9.0).
  • If you specify a build.proj target that implies .NET Framework, then just net462 is used.
  • If you specify a build.proj target that implies .NET, then net8.0 and net9.0 are used.
• The RunFunctionalTestsWindows, RunFunctionalTestsUnix, RunManualTestsWindows, and RunManualTestsUnix targets now runs .NET tests only.
• New RunFunctionalTestsWindowsNetFx and RunManualTestsWindowsNetFx targets were added that run those .NET Framework tests on Windows.
• Scripts and pipelines were updated to use TF where appropriate.

Internal Changes:

• The build.proj targets that imply a Target Framework use new BuildProj and TargetsNetFx properties to control the downstream projects where necessary (i.e. AKV and test projects).
• All projects now use <TargetFrameworks>, even if they only specify a single target framework.
• Fixed filenames for case-sensitive filesystems.
• Removed unnecessary Directory.Build.props files.

Outstanding Issues:

• The BuildTests target still doesn't work (it didn't work before these changes). There is a problem building .NET and .NET Framework targets in parallel.
• The AKV targets on Linux fail to find the .NET Framework reference assemblies after building for .NET, but re-running the .NET Framework targets works. There is likely an issue with the restore process.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 67.71%. Comparing base (6c12daf) to head (701e97a).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...qlClient/Server/SmiEventSink_DeferredProcessing.cs	0.00%	1 Missing ⚠️
...t/netfx/src/Microsoft/Data/SqlClient/SqlCommand.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3311      +/-   ##
==========================================
- Coverage   67.74%   67.71%   -0.04%     
==========================================
  Files         299      293       -6     
  Lines       65564    65254     -310     
==========================================
- Hits        44419    44185     -234     
+ Misses      21145    21069      -76     

Flag	Coverage Δ
addons	?
netcore	72.25% <ø> (+0.11%)	⬆️
netfx	66.17% <0.00%> (-0.02%)	⬇️

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