fix(snackbar): wrap simple snackbar text in span (#12599)

We have begun transforming our html templates in our internal syncs to include our license header
which results in a new line above template. In the simple snack bar this adds a single space when
looking at the elements textContent. By wrapping the content in a span we ensure that the
whitespace is consistent regardless of the presence of the license header comment in the template
file.

Author: josephperrott

src/lib/snack-bar/simple-snack-bar.html

@@ -1,5 +1,4 @@
-{{data.message}}
-
+<span>{{data.message}}</span>
 <div class="mat-simple-snackbar-action"  *ngIf="hasAction">
   <button mat-button (click)="action()">{{data.action}}</button>
 </div>