fix(form-field): remove nonbreaking space before * for required fields (#15490)

The surrounding .mat-form-field-label is already white-space: nowrap so the   doesn't serve any
wrap-preventing function. But it does prevent any trailing <mat-label> spacing from collapsing with
the space before the asterisk, causing for a bad visual appearance of a double space in these cases.

Author: stevenyxu

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">&#32;*</span>
         </label>
       </span>
     </div>

src/lib/input/input.spec.ts

@@ -394,7 +394,7 @@ describe('MatInput without forms', () => {
 
     let el = fixture.debugElement.query(By.css('label'));
     expect(el).not.toBeNull();
-    expect(el.nativeElement.textContent).toMatch(/hello\s+\*/g);
+    expect(el.nativeElement.textContent).toMatch(/hello +\*/g);
   }));
 
   it('should hide the required star if input is disabled', () => {
@@ -407,6 +407,7 @@ describe('MatInput without forms', () => {
 
     expect(el).not.toBeNull();
     expect(el.nativeElement.textContent!.trim()).toMatch(/^hello$/);
+    expect(el.nativeElement.textContent).not.toMatch(/\*/g);
   });
 
   it('should hide the required star from screen readers', fakeAsync(() => {
@@ -424,12 +425,13 @@ describe('MatInput without forms', () => {
 
     let el = fixture.debugElement.query(By.css('label'));
     expect(el).not.toBeNull();
-    expect(el.nativeElement.textContent).toMatch(/hello\s+\*/g);
+    expect(el.nativeElement.textContent).toMatch(/hello +\*/g);
 
     fixture.componentInstance.hideRequiredMarker = true;
     fixture.detectChanges();
 
     expect(el.nativeElement.textContent).toMatch(/hello/g);
+    expect(el.nativeElement.textContent).not.toMatch(/\*/g);
   }));
 
   it('supports the disabled attribute as binding', fakeAsync(() => {