[6.x] Modals

[duncanmcclean]

This pull request updates modals across our application to use the new <Modal> UI component.

In the process, I've also converted buttons/inputs/selects/etc in modals to use UI new versions of those components.

Modal Open/Closed State

This PR also makes some changes to how a modal's open state is controlled.

Previously, modals would open after the user clicked the "trigger". This meant that there wasn't any way to open a modal programatically, or prevent it from closing (in the case of an in-progress AJAX request).

While the modal's open state can still be handled by the model itself, it can now also be opened & closed using v-model bindings:

<!-- When a trigger exists, the modal will handle its own state -->
<Modal>
    <template #trigger>
        <Button text="Open the modal" />
    </template>

    <p>...</p>
</Modal>

<!-- When the :open prop is provided, the parent component will handle the state -->
<script setup>
const modalOpen = ref(true);

function updateOpenState(value) {
    if (ajaxRequestInProgress) {
        return;
    }

    modalOpen.value = value;
}
</script>

<Modal :open="modalOpen" @update:open="updateOpenState">
    <p>...</p>
</Modal>

[duncanmcclean]

@jasonvarga What are your thoughts on the open/close changes in this PR?