* Add Type Definition Provider API

Adds a new API to support type definition providers and adds an initial type definition provider for TypeScript

* Fix comment

* Addressing comments

* Fixer menu option ordering

* Added simple test

* Rename TypeDefinitionProvider to TypeImeplementationProvider

**bug**
In #18346, I originally called the new go to implementation provider api `ImplementationProvider` which we then decided to rename to `TypeDefinitionProvider`. At the time, I didn't realize that a type definition was actually its own, unrelated concept.

**Fix**
Rename `TypeDefinitionProvider` to `TypeImplementationProvider` to make it clear what the purpose and use of this api is.

* Fix a few names in comments

- Basing snippet insertion failure on a new `_codeEditor` null-check.
- Now returns `Thenable<boolean>`.
- Removed vscode.proposed.d.ts copy of the `TextEditor` change.
- Removing empty options interface.

TextEditor.edit snippet overload now returns void. No longer preventing when already in snippet mode.

* 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

Fixes #15583