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

tools/ts-api-guardian/package.json

@@ -17,7 +17,7 @@
     "test": "test"
   },
   "peerDependencies": {
-    "typescript": "~3.8.3"
+    "typescript": "~3.9.2"
   },
   "dependencies": {
     "chalk": "^2.3.1",
@@ -33,7 +33,7 @@
     "chai": "^4.1.2",
     "jasmine": "^3.1.0",
     "source-map-support": "^0.5.9",
-    "typescript": "~3.8.3"
+    "typescript": "~3.9.2"
   },
   "repository": {},
   "keywords": [
@@ -51,4 +51,4 @@
     "url": "https://github.com/angular/angular/issues"
   },
   "homepage": "https://github.com/angular/angular/tools/ts-api-guardian"
-}
+}