testing: initial implementation of continuous run (#170770)

First pass of https://github.com/microsoft/vscode/issues/134941

The UI is pretty minimal so far, just a new icon (though I have a
proposal for some changes in the UX channel.)

If there's more that one profile that supports continuous test runs,
then we open a quickpick and ask the user which ones they want to use.

The data flow is then fairly simple. We call the `profile.runHandler`
with the appropriate request, but just doesn't "track" it like we do for
normal test runs. Then, any `createTestRun` calls are tracked as
ordinary extension-triggered test runs.

Currently we don't do anything to associate these new test runs with the
fact that they were from a specific auto-run request, but that could be
added if need to in the future.

src/vs/workbench/api/common/extHost.api.impl.ts

@@ -384,7 +384,7 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 		// namespace: tests
 		const tests: typeof vscode.tests = {
 			createTestController(provider, label, refreshHandler?: (token: vscode.CancellationToken) => Thenable<void> | void) {
-				return extHostTesting.createTestController(provider, label, refreshHandler);
+				return extHostTesting.createTestController(extension, provider, label, refreshHandler);
 			},
 			createTestObserver() {
 				checkProposedApiEnabled(extension, 'testObserver');
@@ -1370,6 +1370,7 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			LinkedEditingRanges: extHostTypes.LinkedEditingRanges,
 			TestResultState: extHostTypes.TestResultState,
 			TestRunRequest: extHostTypes.TestRunRequest,
+			TestRunRequest2: extHostTypes.TestRunRequest2,
 			TestMessage: extHostTypes.TestMessage,
 			TestTag: extHostTypes.TestTag,
 			TestRunProfileKind: extHostTypes.TestRunProfileKind,