[Property Editor] Support links in docs

Splitting out from https://github.com/flutter/devtools/issues/9034 to address:

> It’d be nice if I could click on things like List and navigate to its definition in my VS Code editor.

Guessing a fair amount of work would be involved here, but filing so that we don't lose track.

Start by reading the parent issue #9034 and the Property Editor context, since this issue names no files, tests, or entry points. Clarify which documentation references should become links, how navigation to definitions should work, and what validation would demonstrate that the feature is complete.

Written by the indexing model from the issue text.