fix(material/stepper): setting invalid value for visibility (#22254)

Setting empty string for visibility is an invalid css property value.
Which leads to error "Failed to execute 'animate' on 'Element' : Partial keyframes are not supported" in old browser.

Author: VinitTomar

src/material/stepper/stepper-animations.ts

@@ -25,9 +25,10 @@ export const matStepperAnimations: {
   /** Animation that transitions the step along the X axis in a horizontal stepper. */
   horizontalStepTransition: trigger('stepTransition', [
     state('previous', style({transform: 'translate3d(-100%, 0, 0)', visibility: 'hidden'})),
-    // Transition to '', rather than `visible`, because visibility on a child element overrides
-    // the one from the parent, making this element focusable inside of a `hidden` element.
-    state('current', style({transform: 'none', visibility: ''})),
+    // Transition to `inherit`, rather than `visible`,
+    // because visibility on a child element the one from the parent,
+    // making this element focusable inside of a `hidden` element.
+    state('current', style({transform: 'none', visibility: 'inherit'})),
     state('next', style({transform: 'translate3d(100%, 0, 0)', visibility: 'hidden'})),
     transition('* => *', animate('500ms cubic-bezier(0.35, 0, 0.25, 1)'))
   ]),
@@ -36,9 +37,10 @@ export const matStepperAnimations: {
   verticalStepTransition: trigger('stepTransition', [
     state('previous', style({height: '0px', visibility: 'hidden'})),
     state('next', style({height: '0px', visibility: 'hidden'})),
-    // Transition to '', rather than `visible`, because visibility on a child element overrides
-    // the one from the parent, making this element focusable inside of a `hidden` element.
-    state('current', style({height: '*', visibility: ''})),
+    // Transition to `inherit`, rather than `visible`,
+    // because visibility on a child element the one from the parent,
+    // making this element focusable inside of a `hidden` element.
+    state('current', style({height: '*', visibility: 'inherit'})),
     transition('* <=> current', animate('225ms cubic-bezier(0.4, 0.0, 0.2, 1)'))
   ])
 };