fix(form-field): remove leading space for asterisk

* In order to align with the 2018 Material Design guidelines, the leading space before the required asterisk should be removed.

Fixes #12721

Author: devversion

src/lib/form-field/form-field.html

@@ -52,7 +52,7 @@
           <span
             class="mat-placeholder-required mat-form-field-required-marker"
             aria-hidden="true"
-            *ngIf="!hideRequiredMarker && _control.required && !_control.disabled">&nbsp;*</span>
+            *ngIf="!hideRequiredMarker && _control.required && !_control.disabled">*</span>
         </label>
       </span>
     </div>