[analyzer] Add a fix for `AMBIGUOUS_EXTENSION_MEMBER_ACCESS`

[asashour]

https://dart-review.googlesource.com/c/sdk/+/252583

---

How to add an extension override for a case like:

extension E on int {
  int get a => 1;
}

extension E2 on int {
  set a(int v) {}
}

f() {
  0.a;
}

In the hints for fixing AMBIGUOUS_EXTENSION_MEMBER_ACCESS in error_fix_status, there is

For each extension, add a fix to add an extension override.
~~

[bwilkerson]

An extension override specifies which extension a member is located in. The receiver is wrapped in parentheses (if it isn't already) and the name of the extension appears before the parenthesized target. In the case above, the fix would change the body of f to either read E(0).a; or E2(0).a;.

Obviously, this only works when the extension is named.

[asashour]

https://dart-review.googlesource.com/c/sdk/+/252583

Thanks a lot for the detailed feedback.