Implement function tearoff equality corner cases #46834
Description
Based on the discussion in dart-lang/language#1712, as a continuation of the work in #46485, and dealing with the test cases added by https://dart-review.googlesource.com/c/sdk/+/205081:
This issue is concerned with the implementation of equality of function objects obtained by function closurization, method closurization, generic function instantiation, and generic method instantiation. The goal is to make the above tests pass.
This change can be enabled without any experiment flags.
Subtasks: