Adds `workbench.workspaceFirstOpen` workspace setting to control applying a default layout
Removes `firstRun` flag from `IDefaultLayout`
Changes `IDefaultEditor` to require a `uri` rather than path+scheme - still supports a fallback until embedders can migrate
Adds `openOnlyIfExists` property to `IDefaultEditor` for better control on if a file should be opened or not

Fixes #96630

Fixes #96639

Fixes #94805

When the panel is maximized over a webview, on reload VS Code calls `.layout` with the dimensions of the editor. However in this case, the dimensions do not match what is actually visible

In this case, the parent element should have zero width so we should  make sure that we do not try giving the webview a width too

Fixes #93332

Fixes #96421

Fixes #96679

make sure editState is CellEditState.Editing when text model changes, also make sure not to duplicate newlines,  #96398

 - ms-vscode.js-debug-nightly -> 2020.4.2917 at 2020-04-30T00:05:41.373Z

Fixes #96527

With the unified reopen-with code, we were no longer calling into the custom editor when reopening a custom editor with the default text editor. This change fixes that by making the custom editor explicitly provide the default editor as one of its overrides