For #94491

- Removes the mime field since it is not used
- Add default snippet
- Slightly improve wording

The canvas and webgl renderers use a flat integer for width whereas
dom uses a floating point number. This was causing canvas/webgl to
be more narrow than they should be. Since changing rendererType is
a pretty infrequent thing it should be fine to resize for this.

Fixes #86425

Fixes #94066

Fixes #94069

Fixes #93384

Fixes #94368

Remove unnecessary command registration.

Fixes #94383

Fixes #94011

fixes https://github.com/microsoft/vscode/issues/94028

Fixes #93995

Fixes #93850

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