This converts the `<AdminPageHeader />` component and the
`<AdminPageSubheader />` components into new components
that can be used outside of admin, and updates the CSS classes.
Also introduces a `<DPageActionButton />` component and child
components for the header action buttons.
I have to keep the old admin-only components around for
now until plugins are updated, then we can remove it,
and remove the re-exports that are done within
admin-page-action-button.gjs
* UX: Apply admin table classes for consistent mobile styling on the emojis page
* UX: remove icon from the button
* UX: styling tweaks on the emoji uploader form
* UX: right align table button controls
* apply prettier
1. Use `this.` instead of `{{action}}` where applicable
2. Use `{{fn}}` instead of `@actionParam` where applicable
3. Use non-`@` versions of class/type/tabindex/aria-controls/aria-expanded
4. Remove `btn` class (it's added automatically to all DButtons)
5. Remove `type="button"` (it's the default)
6. Use `concat-class` helper
