Reduce boxing allocations of `ExtensionMethodInfo` in IDE side

[Youssef1313]

Found 0.9% boxing allocations of ExtensionMethodInfo. Is there a way to reduce that?

[Youssef1313]

I think the fix here is to provide a proper value comparer for the multidictionary.

[ToddGrun]

@Youssef1313 -- I'd like to verify the fix I've got locally. Can you share the repro for which you obtained this profile?