doc(autocomplete-filter): Update example to use Array.prototype.Inclues() (#10779)

Was researching the Auto-complete feature to add it to a project and this little enhancement is more straightforward when dealing with more complex strings.

Current example can't filter words with spaces. By using includes() it can filter full sentences.

src/material-examples/autocomplete-filter/autocomplete-filter-example.ts

@@ -33,7 +33,7 @@ export class AutocompleteFilterExample {
 
   filter(val: string): string[] {
     return this.options.filter(option =>
-      option.toLowerCase().indexOf(val.toLowerCase()) === 0);
+      option.toLowerCase().includes(val.toLowerCase()));
   }
 
 }