[release/10.0] Fix LoaderHeap's free list growing more than expected

[eduardo-vp]

Backport of #129203 to release/10.0

Customer Impact

• Customer reported
• Found internally

This is a regression that impacts apps running test suites, running sometimes even 6x to 8x slower on Linux. Reported in #123124, in particular in this comment #123124 (comment).

Regression

• Yes
• No

Testing

Tested performance with the benchmark provided by the customer and another one in #129203 (comment). The issue happens under a high volume of method instantiations, we don't have such test. We could consider adding one.

Risk

[High/Medium/Low. Justify the indication by mentioning how risks were measured and addressed.]

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.

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Pull request overview

This PR backports the .NET 10 fix for a severe performance regression caused by UnlockedLoaderHeap free-list growth during high-concurrency generic method instantiation. It prevents multiple threads from racing to allocate and then discard redundant InstantiatedMethodDesc allocations, which previously inflated the free list and made subsequent allocations increasingly expensive.

Changes:

• Added a shared helper (SatisfiesMethodConstraintsForInstantiation) to evaluate generic method constraints given an explicit instantiation.
• Changed InstantiatedMethodDesc::NewInstantiatedMethodDesc to hold m_InstMethodHashTableCrst across lookup and creation/insertion, ensuring only one thread allocates/registers a MethodDesc per instantiation.
• Refactored MethodDesc::SatisfiesMethodConstraints to delegate to the new helper.