feat(toast): add htmlAttributes property for passing attributes to buttons (#27855)

Issue number: N/A

---------

## What is the current behavior?
Buttons containing only icons are not accessible as there is no way to
pass an `aria-label` attribute (or any other html attribute).

## What is the new behavior?
- Adds the `htmlAttributes` property on the `ToastButton` interface 
- Passes the `htmlAttributes` to the buttons
- Adds a test to verify `aria-label` and `aria-labelled-by` are passed
to the button

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

core/src/components/toast/toast.tsx

@@ -405,7 +405,14 @@ export class Toast implements ComponentInterface, OverlayInterface {
     return (
       <div class={buttonGroupsClasses}>
         {buttons.map((b) => (
-          <button type="button" class={buttonClass(b)} tabIndex={0} onClick={() => this.buttonClick(b)} part="button">
+          <button
+            {...b.htmlAttributes}
+            type="button"
+            class={buttonClass(b)}
+            tabIndex={0}
+            onClick={() => this.buttonClick(b)}
+            part="button"
+          >
             <div class="toast-button-inner">
               {b.icon && (
                 <ion-icon