Need to revisit how we will handle long running providers

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

Properly implement onDidChangeContent (may be overridden by further refactorings, but simple enough so implementing here for now.) Fixes #89265.

FYI @tyriar

Fixes #89354

fixes #89290

fixes #85975