Finalize the definition link api

- Gives fields more explicit names (target and origin)
- Moves api to vscode.d.ts
- Makes other definition providers (such as type definition provider and implementation provider) also return definition links

Fixes #54101

* Definition link

Add a new `DefinitionLink` type. This type allows definition providers to return additional metadata about a definition, such as the defining span.

Hook up this new provider for typescript

This PR replaces #48001

* Correctly mark field optional

* Small code fixes

- Use lift
- Remove unused param

* Adding documentation

* Add Go To Implementation Api

For #10806

Adds a new API for supporting  `go to implementation` command for languages. Implements an example for TS

* Rename

* Cleanup

* Use Strict Null Checks In TS Extension

Updates the Ts extension to use strict null checks.

* Throw instead of returning undefined in some linkedmap cases

* fix small null check in buffersync

* Fix for request item null