CQ. Extract ElementBindingVisitor from ResolutionVisitor.

ResolutionVisitor previously mixed two responsibilities: binding AST
nodes to prebuilt elements (via ElementWalker) and performing name/type
resolution. This change extracts the binding work into a dedicated
ElementBindingVisitor and makes ResolutionVisitor assume fragments and
annotations are already attached.

- Add ElementBindingVisitor to attach declaredFragment/elementAnnotation
  for declarations, parameters, local variables, labels, and generic
  function types, and to synthesize metadata when needed.
- Run the binding visitor up-front in LibraryAnalyzer and in summary
  resolvers (AstResolver/ConstructorInitializerResolver) when resolving
  isolated subtrees such as annotations, expressions, and initializers.
- Simplify ResolutionVisitor by removing ElementWalker/ElementHolder
  plumbing and focusing it on name/type resolution and AST rewrites.
- Harden visitors that may see unbound nodes in recovery by
  short-circuiting when declared fragments are missing, and use
  enclosingElement for local-parameter checks.

This separation improves maintainability and enables correct partial
resolution by ensuring local fragments and metadata exist before the
resolver runs.

Change-Id: If7a8b82f1e280cc7d6e072e8275e821d70bf2883
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/481001
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>