Create a temporary overload for testing `CustomEditor`. In finalization, we'd update `registerCustomEditorProvider` to take both types of custom editor instead

For #77131

The team would like to discuss this API further before finalizing it. `CustomTextEditor` will still be finalized this iteration

Fix #93815

Fixes #94061

Fix #93618

For #77131

#85992

This reverts commit 51a62012.

`SemanticTokensBuilder`: Add `push` overload that accepts objects and support out-of-order calls (for #93614)

* Expose more shared properties from TextDocument on CustomDocument

Copies some shared properties from `TextDocument` to `CustomDocument`. We may want to consider this since `CustomDocument` is intented to be subclassed, and there is the risk after shipping the custom editor api that one of these subclasses could implement a property/method such as `version` which would break if we added a `CustomDocument.version` property at a later time

Call it `joinPath`, add tests, don't reuse the implemention from resources.ts, https://github.com/microsoft/vscode/issues/90208

For #77131

- Use a class for `CustomDocument` instead of an interface. Extensions can now add their own data to a `CustomDocument` by sublassing

- Renamed `resolveCustomDocument` to `openCustomDocument` and require that extensions return a `CustomDocument`

- Exposed edits on `CustomDocument`

- Made the third parameter of `registerCustomEditorProvider` a generic options bag that takes a `webviewOptions`

Separates the tree rendering from the data model cache
Fixes many issues and simplifies the code