Commit(s) to merge

e6e9b4e

Target

stable

Prepared changelist for beta/stable

https://dart-review.googlesource.com/369241

Issue Description

A bug in the dart2wasm compiler can lead to a type parameter type to have incorrect nullability

What is the fix

Fix sharing of type parameter values with super types if nullability is changed.

Why cherry-pick

External user hit this (#55741)

Risk

Low

Issue link(s)

#55741

Extra Info

No response