[release/6.0] ComponentModel threading fixes

[steveharter]

Backport of #104407 and #103835 to release/6.0.

See also #107353 for the 8.0 port.

Customer Impact

Fixes various threading issues with TypeDescriptor and PropertyDescriptor.

Regression

Yes; a previous servicing fix caused concurrency issues with:

• Dictionary\hashtable concurrency issues reported in Assertion failed under System.ComponentModel.TypeDescriptor.CheckDefaultProvider #104221 and NuGet restore failing with NullReferenceException #103823 and this port addresses those by using ConcurrentDictionary.
• A rare deadlock could occur as reported in Long running System.ComponentModel tests #103265.

Testing

The 9.0 tests that were added are ported here.

Risk

Low; the fixes have been in 9.0 for several months with no reported regressions.

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[steveharter]

/ba-g CI test failures appear unrelated:

x86 Release Libraries_NET48
Git fetch failed with exit code: 128
Publishing build artifacts failed with an error: Not found PathtoPublish: D:\a_work\1\s\artifacts\log\

Linux
Work item System.IO.Net5Compat.Tests
Work item System.IO.Tests

Browser wasm Release
Work item Common.Tests
Work item IcuAppLocal.Tests
Work item Invariant.Tests
Work item Microsoft.Bcl.AsyncInterfaces.Tests
Work item Microsoft.CSharp.Tests

[carlossanlop]

Friendly reminder that Code Complete for the October Release is September 9. If we want this fix to be included in that release, please merge this PR before that date.

[carlossanlop]

There were many unknown/new failures in this PR. are any of them known? Maybe re-run could clean them up?

[steveharter]

There were many unknown/new failures in this PR. are any of them known? Maybe re-run could clean them up?

A re-run didn't help. The bulk are linux. Also, this other PR has more or less the same failures: #106220

[steveharter]

/ba-g CI test failures appear unrelated