Add FreeBSD as valid test host.

[Thefrank]

This adds missing FreeBSD case to coreclr_arguments.py as a valid test host and adds FreeBSD to run.py
Creates TestLibrary.Utilities.IsFreeBSD where needed for the remaining tests

[Thefrank]

Python returns a freebsd with major OS version when using sys.platform (e.g. freebsd14)

The default coredump file on FreeBSD is %N.core. Which is not as useful as other Unixy system's core.%P. kern.corefile can only be changed by root at the host-kernel level and this is reflected across all guest jails.

Results: src/tests/build.sh Debug /p:LibrariesConfiguration=Debug -rebuild -runtests -priority1

Time [secs] | Total | Passed | Failed | Skipped | Assembly Execution Summary
============================================================================
     81.863 |    76 |     76 |      0 |       0 | GC.API.XUnitWrapper.dll
     11.855 |     3 |      3 |      0 |       0 | GC.Coverage.XUnitWrapper.dll
    212.662 |    42 |     41 |      1 |       0 | GC.Features.XUnitWrapper.dll
     36.716 |     6 |      6 |      0 |       0 | GC.LargeMemory.XUnitWrapper.dll
     47.813 |    12 |     12 |      0 |       0 | GC.Regressions.XUnitWrapper.dll
    150.765 |   482 |    482 |      0 |       0 | GC.Scenarios.XUnitWrapper.dll
      0.014 |     1 |      1 |      0 |       0 | GC.Stress.XUnitWrapper.dll
      4.529 |     1 |      1 |      0 |       0 | ilasm.PortablePdb.XUnitWrapper.dll
      5.351 |     1 |      1 |      0 |       0 | ilasm.System.XUnitWrapper.dll
     31.784 |     1 |      1 |      0 |       0 | ilverify.XUnitWrapper.dll
      6.177 |     2 |      2 |      0 |       0 | profiler.assembly.XUnitWrapper.dll
     13.317 |     2 |      2 |      0 |       0 | profiler.elt.XUnitWrapper.dll
      6.446 |     3 |      3 |      0 |       0 | profiler.eventpipe.XUnitWrapper.dll
      8.058 |     4 |      4 |      0 |       0 | profiler.gc.XUnitWrapper.dll
      8.126 |     1 |      1 |      0 |       0 | profiler.gcheapenumeration.XUnitWrapper.dll
      5.612 |     1 |      1 |      0 |       0 | profiler.handles.XUnitWrapper.dll
      0.018 |     1 |      1 |      0 |       0 | profiler.multiple.XUnitWrapper.dll
      0.017 |     1 |      1 |      0 |       0 | profiler.rejit.XUnitWrapper.dll
     20.539 |     1 |      1 |      0 |       0 | profiler.transitions.XUnitWrapper.dll
     12.248 |     5 |      4 |      1 |       0 | profiler.unittest.XUnitWrapper.dll
----------------------------------------------------------------------------
    663.910 |   646 |    644 |      2 |       0 | (total)


Creating repro files at: /root/runtime/artifacts/log/repro
Writing repro: /root/runtime/artifacts/log/repro/GC/Features/Finalizer/finalizeio/finalizeio/repro_finalizeio.sh
Writing repro: /root/runtime/artifacts/log/repro/profiler/unittest/metadatagetdispenser/repro_metadatagetdispenser.sh
Repro files written.

Log files at: /root/runtime/artifacts/log
Repro files at: /root/runtime/artifacts/log/repro
Tests run successful.

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[am11]

👍

[emaste]

These changes LGTM