fix(alert): match MD spec on tablet (#28501)

Issue number: resolves #23977

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issue. -->

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## What is the current behavior?
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The MD Alert on tablet dimensions does not match the MD spec

## What is the new behavior?
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this PR. -->

- MD Alert now follows the MD spec for tablet dimensions
- Added tablet and mobile viewport mixins for alert and the card modal.
(There should be no visual diffs for the card modal)

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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and migration path for existing applications below. -->


## Other information

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screenshots of how the component looks before and after the change. -->

This supersedes https://github.com/ionic-team/ionic-framework/pull/27462
since I needed to add new screenshot tests. The author of that PR has
been given co-author credit here.

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Co-authored-by: GlenOttley <GlenOttley@users.noreply.github.com>
Co-authored-by: ionitron <hi@ionicframework.com>
Co-authored-by: Brandy Carney <brandyscarney@users.noreply.github.com>

core/src/components/modal/modal.ios.scss

@@ -27,7 +27,7 @@
 // iOS Card Modal
 // --------------------------------------------------
 
-@media screen and (max-width: 767px) {
+@include mobile-viewport() {
   @supports (width: max(0px, 1px)) {
     :host(.modal-card) {
       --height: calc(100% - max(30px, var(--ion-safe-area-top)) - 10px);
@@ -60,7 +60,7 @@
   }
 }
 
-@media screen and (min-width: 768px) {
+@include tablet-viewport() {
   :host(.modal-card) {
     --width: calc(100% - 120px);
     --height: calc(100% - (120px + var(--ion-safe-area-top) + var(--ion-safe-area-bottom)));