[Unquoted Imports] Analyzer Implementation

[kallentu]

This meta issue tracks all the analyzer implementation work items. Referenced from: https://github.com/dart-lang/sdk/blob/main/pkg/analyzer/doc/process/new_language_feature.md

WIP below -- haven't evaluated each part yet.

• AST enhancements (AstBuilder)
• Resolution of directives
• Element model
• Type system updates
• Summary support
• Resolution
  • ResolutionVisitor (resolve types)
  • ScopeResolverVisitor (resolve simple identifiers by scope)
  • ResolverVisitor (type-based resolution)
• Constant evaluation
• Index and search
• Warnings (annotation-based, unused*, strict-mode-based, a few others)
  • OverrideVerifier and InheritanceOverrideVerifier (report errors and warnings related to overrides)
  • ErrorVerifier (report other errors and warnings)
  • FfiVerifier (report errors and warnings related to FFI)
  • Unused elements warnings
• ExitDetector
• NodeLintRegistry