- Initial version of custom views and tree data provider API

- Adopt proposed API to contribute explorer views
- Adopt extension host and main to contribute explorer views
- Implement contributable views in explorer viewlet

From: https://github.com/Microsoft/TypeScript/issues/15352

TS 2.3.1 introduced a breaking change by [switching to covariant types for callbacks](https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#covariance-in-callback-parameters). This change tries to fix these compiler errors in the workbench codebase

Changes pinned property to preview
Adds ITextDocumentShowOptions as main-side DTO

Moves column into the options
Removes overloads from the proxy

- API to create a view passing the data provider
- Have methods on created API to refresh

- A new approach to register tree node
- Support on change listener to refresh node

fixes #24009

fixes #2824

* 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