fix(button): don't use divs in button template (#20376)

* fix(button): don't use divs in button template

* address feedback

Author: mmalerba

src/material-experimental/mdc-button/button.html

@@ -9,7 +9,7 @@
   The indicator can't be directly on the button, because MDC uses ::before for high contrast
   indication and it can't be on the ripple, because it has a border radius and overflow: hidden.
 -->
-<div class="mat-mdc-focus-indicator"></div>
+<span class="mat-mdc-focus-indicator"></span>
 
 <ng-content select=".material-icons[iconPositionEnd], mat-icon[iconPositionEnd]">
 </ng-content>

src/material/button/button.html

@@ -1,7 +1,7 @@
 <span class="mat-button-wrapper"><ng-content></ng-content></span>
-<div matRipple class="mat-button-ripple"
-     [class.mat-button-ripple-round]="isRoundButton || isIconButton"
-     [matRippleDisabled]="_isRippleDisabled()"
-     [matRippleCentered]="isIconButton"
-     [matRippleTrigger]="_getHostElement()"></div>
-<div class="mat-button-focus-overlay"></div>
+<span matRipple class="mat-button-ripple"
+      [class.mat-button-ripple-round]="isRoundButton || isIconButton"
+      [matRippleDisabled]="_isRippleDisabled()"
+      [matRippleCentered]="isIconButton"
+      [matRippleTrigger]="_getHostElement()"></span>
+<span class="mat-button-focus-overlay"></span>