Switch internal VS Code tests off of NotebookContentProvider api

[mjbvz]

The notebook content provider api is being removed: #147248

However it looks like a few of our tests are still using it:

vscode/extensions/vscode-api-tests/src/singlefolder-tests/notebook.kernel.test.ts

Lines 88 to 89 in 07025f0

	const apiTestContentProvider: vscode.NotebookContentProvider = {
	openNotebook: async (resource: vscode.Uri): Promise<vscode.NotebookData> => {

vscode/extensions/vscode-api-tests/src/singlefolder-tests/notebook.api.test.ts

Line 78 in a2cd34f

const apiTestContentProvider: vscode.NotebookContentProvider = {

vscode/extensions/vscode-api-tests/src/singlefolder-tests/notebook.document.test.ts

Line 23 in 07025f0

const complexContentProvider = new class implements vscode.NotebookContentProvider {

vscode/extensions/vscode-notebook-tests/src/extension.ts

Line 23 in ac05ae7

context.subscriptions.push(vscode.workspace.registerNotebookContentProvider('notebookSmokeTest', {

[rebornix]

Along with the use of content provider in tests, we also need to remove the content provider used by Interactive Window.