[RuntimeAsync] Removing TODO in methodtablebuilder.cpp. More robust insertion of methods.

[VSadov]

Fixes: #121760

To make the insertion of methods more robust we:

• double the capacity of the MT builder up to the absolute limit required by the implementation of MethodDesc.
• check if we still fit in the budget when adding methods.

Note: it may result in some programs that used to run to start throwing TypeLoadException.

These would be extreme cases though. The capacity for simple methods is implementation-specific. In CoreCLR a type cannot contain more than 65524 methods due to internal limitations.
(More complex cases involving inheritance/virtual methods may have additional limits.)

With runtime async, methods that return Task/ValueTask may consume 2 methods instead of 1 from this 65524 budget.
In a worst case where all methods return Task, the limit becomes 32762 methods in a single type, which still seems a very high limit for reasonably real programs that are not generated testcases.

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[Copilot]

Pull request overview

This PR removes a TODO comment in methodtablebuilder.cpp and makes the insertion of async method variants more robust by implementing proper capacity management and bounds checking. The changes enable RuntimeAsync by default and add comprehensive tests to verify the new method capacity limits.

• Implements robust capacity doubling for async methods (up to MAX_SLOT_INDEX - 1 = 65524)
• Adds runtime bounds checking before method insertion to prevent array overflow
• Enables RuntimeAsync by default for CoreCLR and enables corresponding tests

Reviewed changes

Copilot reviewed 6 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/coreclr/vm/methodtablebuilder.cpp	Replaces conditional capacity doubling with robust upfront capacity calculation clamped to MAX_SLOT_INDEX - 1, and adds bounds check before method insertion to throw TypeLoadException when limit is exceeded
src/coreclr/utilcode/allocmemtracker.cpp	Increases consistency check threshold from 10,000 to 60,000 blocks to accommodate larger classes with up to 65,524 methods
src/coreclr/inc/clrconfigvalues.h	Enables RuntimeAsync feature by default (changes default value from 0 to 1)
src/tests/async/Directory.Build.targets	Removes the DisableProjectBuild condition to enable async tests for CoreCLR (non-nativeaot) builds
src/tests/async/capacity/capacity.csproj	Defines new test project structure including test file and three generated test class files
src/tests/async/capacity/capacity.cs	Adds three test scenarios: 40,000 int-returning methods (should succeed), 32,750 Task-returning methods (should succeed), and 32,763 Task-returning methods (should fail with TypeLoadException)

[jkotas]

LGTM otherwise. Thanks!

[VSadov]

/ba-g failures in LibraryImportGenerator are all #122447

[VSadov]

Thanks!