build: prepare for TypeScript 3.9 (#36989)

- Fix several compilation errors
- Update @microsoft/api-extractor to be compatible with TypeScript 3.9

PR Close #36989

integration/BUILD.bazel

@@ -80,6 +80,12 @@ INTEGRATION_TESTS = {
     "service-worker-schema": {},
     "side-effects": {"tags": ["no-ivy-aot"]},
     "terser": {},
+    "typings_test_ts39": {
+        # Special case for `typings_test_ts39` test as we want to pin
+        # `typescript` at version 3.9.x for that test and not link to the
+        # root @npm//typescript package.
+        "pinned_npm_packages": ["typescript"],
+    },
 }
 
 [