Handle delayed Notebook provider registration (#3526)

* Handle delayed Notebook provider registration
- Fixes #3197 Notebooks: builtin provider always used on reopen with notebook file visible
- Fixes #3414 Can't refresh kernel after connect to big data cluster

There are 3 parts to this fix:
- If no notebook provider other than the default is installed, we warn users and prompt to install the SQL2019 extension
- We wait on the extension host registration to complete before determining which provider to use
- We know that the extension registration of the provider instance will be after package.json is read, so if we wait after registration for 10 seconds to give this a chance to happen before returning a provider to the front end

* Remove launch.json change that was added accidentally

* Fix timeout not being the expected value

* Removed console log left in during debugging

* Remove unnecessary whitespace

* Fix unit test failure

* Name the registration better, and remove outdated comments

src/sql/workbench/api/node/mainThreadNotebookDocumentsAndEditors.ts

@@ -258,7 +258,8 @@ export class MainThreadNotebookDocumentsAndEditors extends Disposable implements
 		extHostContext: IExtHostContext,
 		@IInstantiationService private _instantiationService: IInstantiationService,
 		@IEditorService private _editorService: IEditorService,
-		@IEditorGroupsService private _editorGroupService: IEditorGroupsService
+		@IEditorGroupsService private _editorGroupService: IEditorGroupsService,
+		@INotebookService private readonly _notebookService: INotebookService
 	) {
 		super();
 		if (extHostContext) {
@@ -306,7 +307,7 @@ export class MainThreadNotebookDocumentsAndEditors extends Disposable implements
 		if(!providerId)
 		{
 			// Ensure there is always a sensible provider ID for this file type
-			providerId = getProviderForFileName(uri.fsPath);
+			providerId = getProviderForFileName(uri.fsPath, this._notebookService);
 		}
 
 		model.providerId = providerId;