Fixes #35524 (80% solution)

This PR makes the parser parse @link tag and the language service offer symbols for entity names found at the beginning of those tags. Links are stored redundantly with comment text, so they're only used to provide (1) a span to an editor to format in some way (2) a symbol for the declaration of the link's target.

Future PRs

1. Parse # as type-space element access: Class#method. As well as, possibly, the normal TS syntax Class["method"], which doesn't currently parse either.

Open questions

1. I parse @see {@link ...} as a @see with no reference and a link in its comment text. I think that's OK.
2. I intentionally do not parse { @link X}, with a space separating { and @. I saw this only twice in my corpus, but @amcasey points out that it's easy to support with an additional skipWhitespace call. I originally skipped it because I had slightly less lookahead when the next token after { was @, but that made the code unreadable, so I dropped it.

Resolved questions

1. I introduced JSDocText and JSDocLink nodes into the AST, which better reflects the semantic relation of comments to their tags. It is more expensive, though, it means that jsdoc comment text is treated as a first-class member of the parse tree now.

Thanks for the PR! It looks like you've changed the TSServer protocol in some way. Please ensure that any changes here don't break consumers of the current TSServer API. For some extra review, we'll ping @sheetalkamat, @amcasey, @mjbvz, @minestarks for you. Feel free to loop in other consumers/maintainers if necessary

@mjbvz and @amcasey, you should maybe also look at this (at least the protocol part)

@typescript-bot pack this

Only thing I’m curious about is if there are some places where JSDoc can go, but otherwise entity names could not go, and therefore might expose a hole in getSymbolAtLocation.

Heya @andrewbranch, I've started to run the tarball bundle task on this PR at fce33f1. You can monitor the build here.

@andrewbranch I indeed tried writing more tests and discovered a hole. I'll put up a commit that makes getSymbolAtLocation work with identifiers in links.

@jessetrinity any chance you could validate this doesn't break anything in VS? I don't think we'll just get @link tag support for free, but at least JSDoc tags and other stuff should continue to work (in plain .js / .html / .cshtml)

The most recent commit avoids breaking VS, and I'm working on tests for all 4 possible combinations of the rich/full matrix.

This is ready for review now.

The behavior and interface changes generally LGTM. Some suggestions below.

I think this PR has had enough review to be ready to use. I'll merge it and address any follow-up in subsequent PRs.

Cool!

Docs can be updated now https://www.typescriptlang.org/docs/handbook/jsdoc-supported-types.html