[vm] Implement function canonicalization corner cases

[eernstg]

This is the VM specific issue for #46485, which has the details.

[dcharkes]

I have approved VM failures on this issue.

language/generic_methods/explicit_instantiated_tearoff_test: https://dart-ci.appspot.com/log/vm-kernel-precomp-nnbd-mac-release-arm64/dartkp-strong-mac-release-arm64/2/language/generic_methods/explicit_instantiated_tearoff_test

language/closure/identity_equality_tearoff_test:
https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket.appspot.com/8843117657258310224/+/u/test_results/new_test_failures__logs_

[eernstg]

Thanks, @dcharkes!

Checking language/generic_methods/explicit_instantiated_tearoff_test.dart, I can see that these are cases using the new explicit generic instantiation of functions, and the expectations are in line with the newly specified behavior. So fixing this issue might well cause language/generic_methods/explicit_instantiated_tearoff_test.dart to succeed as well.

Regarding language/generic_methods/explicit_instantiated_tearoff_test.dart: I'm not sure why that one would need approval, I just approved it when I landed it yesterday, and the 'Results' page did not show that test as needing any further approvals when I checked. But maybe the approval was needed for a couple of configurations that weren't covered by the trybots, and you just did it before I saw the problem. Thanks again! ;-)

[leafpetersen]

I believe this changed is gated on some further discussion, see here.

[alexmarkov]

Both language/generic_methods/explicit_instantiated_tearoff_test and language/closure/identity_equality_tearoff_test are currently passing in all configurations, so tentatively closing the issue.