Previous related issue: #2477
Previous related PR: astral-sh/ruff#22837

We recently improved hover for subscript literals (e.g. TypedDict keys). A natural follow‑up is to support go‑to‑declaration for these keys, so cmd+click on person["name"] jumps to the corresponding field in the TypedDict definition.

Notes:

• This likely needs a distinct GotoTarget for literal subscripts so goto‑declaration can specialize behavior.
• Focus on TypedDict keys; other subscripts probably don’t have a meaningful declaration target.