Implements many API review changes
Fixes #89558

Part of #75793

Part of #75793

fixes microsoft/vscode-remote-release#2115

Cleans up API and removes some unused features (e.g. paging)
Adds date formatting
Adds loading progress and message
Removes lots of console.logs 😁
Adds titles to diffs

Adds a backup method to the custom editor API proposal. This method allows custom editors to hook in to VS Code's hot exit behavior

If `backup` is not implemented, VS Code will assume that the custom editor cannot be hot exited.

When `backup` is implemented, VS Code will invoke the method after every edit (this is debounced). At this point, this extension should back up the current resource.  The result is a promise indicating if the backup was successful or not

VS Code will only hot exit if all backups were successful.

For #88719

With this change, instead of passing custom editor edit json back and forth with the extension host, we keep the original edit objects on the extension host. This means that we can pass extensions back the exact same edit object they first hand to us. It also means that edits no longer need to be json serializable.

- extract a separate DocumentRangeSemanticTokensProvider that deals with a document range
- extract a separate provideDocumentSemanticTokensEdits that deals with updating via SemanticTokensEdits a previous result

Part of #81388

Part of #81388

Part of #81388