build: correct tsconfig.app.json file includes

This appears to have been broken in the upgrade to angular 9 in 2020:
f9d9454034 (diff-90318a63edd01d7a315da6833f32e2c4f30c4048067598f0cd7b3be879963895)

By only including the entrypoint "main.ts" in the files list, without
any include glob, no downstream files can be associated with the
tsconfig project file until the 'main.ts' entrypoint has been opened in
the editor. As a result, language service features are limited. For
example, in VSCode:

1. Close all editor files
2. Run "Developer: Reload window"
3. Open app.component.ts
4. right click on `AppComponent` and click "Find All References"

The references result will _not_ include 'main.ts' as it should. The
typescript language service is able to provide only basic language
features (which excludes full type checking, references, path alias
resolution, etc) until the file can be associated with a tsconfig.

In addition, the Angular Language Service cannot operate until the
`main.ts` file has been opened to associate the application files with
the `tsconfig.app.json`.

This update more closely matches the `tsconfig.app.json` template used
for new Angular projects, found here:
672ae14cd2/packages/schematics/angular/application/files/common-files/tsconfig.app.json.template

src/tsconfig.app.json

@@ -7,7 +7,14 @@
     "allowSyntheticDefaultImports": true
   },
   "files": ["main.ts", "polyfills.ts"],
-  "include": ["**/*.d.ts"],
+  "include": ["app/**/*.ts"],
+  "exclude": [
+    "**/*.spec.ts",
+    "**/*.worker.ts",
+    "**/__mocks__/**",
+    "**/test-utils.ts",
+    "app/util/**/*.ts"
+  ],
   "angularCompilerOptions": {
     "fullTemplateTypeCheck": true,
     "strictInjectionParameters": true