UNDR. Report failed name lookups through LookupFailureReporter.

This is the first step toward the diagnostics proposed in
https://github.com/dart-lang/sdk/issues/64411: report a failed lookup by
the namespace that was searched and the capability that was required,
read or write, not by the syntax.

Call sites now describe a failure with a `LookupDomain`, such as
`InstanceLookupDomain` for `x.foo` or `SuperLookupDomain` for
`super.foo`, and for writes with the declaration found instead of a
setter. Each domain chooses its diagnostics, still the existing codes,
so that later changes replace the codes of one domain at a time.
`LookupFailureReporter` applies the rules shared by all lookups.

`AssignmentVerifier` is folded into the reporter, and `ErrorVerifier` no
longer repeats the resolver's checks of for-each targets.

Behavior changes, where a rule applied to only some lookups:
- Synthetic names are never reported, so `{.}` no longer has a second
  diagnostic for the empty name.
- Names that might come from a missing library, as in
  `import 'a.dart' show x`, are not reported for writes, pattern
  assignments, and implicit `this` invocations either.
- A function-type alias is named with its import prefix in all
  messages, also for `a.Fn.foo`.

Bug: https://github.com/dart-lang/sdk/issues/64411
Change-Id: Ie76b882d74164bc01d8b79a0fc4aa9f4743406d1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/561102
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>