Simplified MinOpts GC ref tracking. (dotnet/coreclr#9231)

Simplified MinOpts GC ref tracking. (dotnet/coreclr#9231)

Simplified MinOpts GC ref tracking - when a method is compiled with MinOpts for targets with the 64-bit GC info encoder we mark all GC slots as untracked and we omit encoding call sites with no live tracked GC refs explicitly in the GC tables; this can be controlled using the new COMPlus_JitMinOptsTrackGCrefs environment flag.

Commit migrated from https://github.com/dotnet/coreclr/commit/d7509df9635ca92c1a3cf75dc2516ae51b0e03d6