docs(contact-chips): improve the comments about highlighting (#11362)

using md-highlight-text on contact chips actually breaks the component
only md-highlight-flags is supported on contact chips
add md-highlight-flags example to mdHighlightDirective docs

Relates to #8142

Author: Splaktar

src/components/autocomplete/js/highlightDirective.js

@@ -24,7 +24,7 @@ angular
  * <hljs lang="html">
  * <input placeholder="Enter a search term..." ng-model="searchTerm" type="text" />
  * <ul>
- *   <li ng-repeat="result in results" md-highlight-text="searchTerm">
+ *   <li ng-repeat="result in results" md-highlight-text="searchTerm" md-highlight-flags="i">
  *     {{result.text}}
  *   </li>
  * </ul>

src/components/chips/js/contactChipsDirective.js

@@ -13,8 +13,9 @@ angular
  * returns  a list of possible contacts. The user can select one of these and add it to the list of
  * chips.
  *
- * You may also use the `md-highlight-text` directive along with its parameters to control the
- * appearance of the matched text inside of the contacts' autocomplete popup.
+ * You may also use the <a ng-href="api/directive/mdHighlightText">md-highlight-flags</a> attribute
+ * along with its parameters to control the appearance of the matched text inside of the contacts'
+ * autocomplete popup.
  *
  * @param {expression} ng-model Assignable AngularJS expression to be data-bound to the list of
  *    contact chips. The expression should evaluate to an `Object` Array.