Add ts to globalThis in run.js for convenience during debugging

In namespaces, we'd have access to a variable named "ts" when debugging,
because that was just the ts namespace in the current file. But when
modules, that variable doesn't exist, either because we are pure modules
(so no ts variable), or named something else (when bundled, for export).

Tack a "ts" object onto the globals, which should make this easier. Of
course, someone may eventually declare a variable in the top level scope
named "ts" and break this, but we can cross that bridge when we come to
it.

src/testRunner/runner.ts

@@ -280,6 +280,9 @@ function beginTests() {
 
 export let isWorker: boolean;
 function startTestEnvironment() {
+    // For debugging convenience.
+    (globalThis as any).ts = ts;
+
     isWorker = handleTestConfig();
     if (isWorker) {
         return Parallel.Worker.start();