[MaterialAlertDialog] Custom spacing between action buttons and content

For a simple dialog with a single line of text there is way too much of a gap between message and action buttons.

I could reduced the spacing a bit using:

    <dimen name="m3_alert_dialog_action_top_padding" tools:override="true">0dp</dimen>

Original spacing:

Reduced spacing:

That's still much spacing but tolerable I guess.

Things could be improved further if we could override the minHeight from contentPanel in m3_alert_dialog.xml which is currently hardcoded to 48dp.

See https://github.com/material-components/material-components-android/issues/4345#issuecomment-3592444076.

I guess we would need something like:

<dimen name="m3_alert_dialog_content_min_height">48dp</dimen>

That would allow apps to override it.