[release/10.0] Reduce contention in UnwindInfoTable seen during high volume LCG method creation (#129035)

Backport of #128619 to release/10.0

/cc @eduardo-vp

## Customer Impact

- [x] Customer reported
- [ ] Found internally

This regression causes test suites to run up to 1.7x slower on Windows
in .NET 10. Issue originally reported in
#123124.

## Regression

- [x] Yes
- [ ] No

## Testing

The fix was verified using two benchmarks mentioned in the original PR.
I think this is very specific to situations where a high volume of LCG
methods are created simultaneously which explains why the issue was
previously missed.

## Risk

Medium. It changes the behavior of `UnwindInfoTable` to fix the
regression. However, the change has been in main for ~3 weeks and no
issues have been linked to this PR.

**IMPORTANT**: If this backport is for a servicing release, please
verify that:

- For .NET 8 and .NET 9: The PR target branch is `release/X.0-staging`,
not `release/X.0`.
- For .NET 10+: The PR target branch is `release/X.0` (no `-staging`
suffix).

## Package authoring no longer needed in .NET 9

**IMPORTANT**: Starting with .NET 9, you no longer need to edit a NuGet
package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older
versions.

---------

Co-authored-by: Eduardo Velarde <evelardepola@microsoft.com>
Co-authored-by: Eduardo Velarde <32459232+eduardo-vp@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: 4 people