Add [ThreadStatic] correctness analyzers

[stephentoub]

Fixes dotnet/runtime#46626

Note that we'd discussed adding a fixer for the case of [ThreadStatic] applied to an instance field, but on further thought I don't think that's a good idea. If someone is using [ThreadStatic] on an instance field, it's possible it's a mistake and they intended for it to be static, but it's also quite likely they assumed it would create a per-thread instance value (as you might get with ThreadLocal<T>) so providing a fix to just mark it static would potentially lead someone down the wrong path, and just adding static is trivial for someone to do. There should also be very few violations of this, so a bulk fix isn't going to be meaningful.

[codecov]

Codecov Report

Merging #5920 (9e05a37) into main (2b89a41) will decrease coverage by 0.00%.
The diff coverage is 96.44%.

@@            Coverage Diff             @@
##             main    #5920      +/-   ##
==========================================
- Coverage   96.03%   96.03%   -0.01%     
==========================================
  Files        1310     1312       +2     
  Lines      302825   302990     +165     
  Branches     9572     9579       +7     
==========================================
+ Hits       290808   290964     +156     
- Misses       9733     9739       +6     
- Partials     2284     2287       +3     

[Youssef1313]

Edge cases to consider whether they should be supported:

using System;

public class C
{
    [field: ThreadStatic]
    public string S { get; }

    [field: ThreadStatic]
    event EventHandler E;
}

public record R([field: ThreadStatic] string S);

[stephentoub]

Edge cases to consider whether they should be supported:

I added support for properties (which implicitly adds support for records). I don't believe it's possible today to find the backing field for an IEventSymbol.

[stephentoub]

Thanks for reviewing, @Youssef1313.