refactor(docs-infra): fix docs examples for Angular-specific tslint rules (#38143)

This commit updates the docs examples to be compatible with the
following Angular-specific tslint rules:
- `component-selector`
- `directive-selector`
- `no-conflicting-lifecycle`
- `no-host-metadata-property`
- `no-input-rename`
- `no-output-native`
- `no-output-rename`

This is in preparation of updating the docs examples `tslint.json` to
match the one generated for new Angular CLI apps in a future commit.

PR Close #38143

aio/content/examples/testing/src/app/demo/demo.ts

@@ -1,4 +1,4 @@
-/* tslint:disable:forin */
+// tslint:disable: directive-selector forin no-input-rename
 import { Component, ContentChildren, Directive, EventEmitter,
          Injectable, Input, Output, Optional,
          HostBinding, HostListener,

aio/content/examples/testing/src/app/shared/highlight.directive.ts

@@ -1,3 +1,4 @@
+// tslint:disable: directive-selector
 // #docregion
 import { Directive, ElementRef, Input, OnChanges } from '@angular/core';
 

aio/content/examples/testing/src/testing/router-link-directive-stub.ts

@@ -3,7 +3,7 @@ import { Directive, Input, HostListener } from '@angular/core';
 // export for convenience.
 export { RouterLink} from '@angular/router';
 
-/* tslint:disable:directive-class-suffix */
+// tslint:disable: directive-class-suffix directive-selector
 // #docregion router-link
 @Directive({
   selector: '[routerLink]'