Remove raw analysis sink pointers from TypeChecker

[arniber21]

What to build

Replace the type checker's raw mutable annotation and resolution sink pointers with a safe ownership or borrowing design. IDE analysis must collect the same type annotations and resolved references without lifetime erasure or undocumented aliasing assumptions.

Acceptance criteria

• TypeChecker contains no raw pointers for annotation or resolution output.
• Analysis callers cannot retain a checker beyond the lifetime of its sinks.
• Type checking without IDE analysis does not allocate or clone analysis output unnecessarily.
• Existing hover, references, rename, diagnostics, and typed-program tests retain their behavior.
• The frontend has no unsafe block related to analysis sinks.

Blocked by

None - can start immediately.

[arniber21]

Implemented and merged via PR. Closing as complete.