Add "Push folders" settings screen that prompts for alarm permission

[cketti]

Change the UI for the "Push folders" setting to ask for the permission to schedule exact alarms before allowing the user to enable Push.

It's possible to end up in a state where Push is enabled but the permission is missing. That's why we always allow the user to select the None option to disable Push, even when the permission hasn't been granted.

The plan is to change the way Push is enabled for folders (#7761). So almost all of this code is going to be removed in the near future.

Test instructions

• Use an Android 14 device.
• Set up an IMAP account.
• Go to Settings → [Account] → Fetching mail → Push folders.
  • On a fresh install the permission to schedule alarms won't have been granted. So the permission text + button should be visible.
  • Once the permission has been granted, only the radio buttons should be visible. All of them should be enabled and selectable.
  • To test the case where Push is enabled (the setting has a value other than None) but the permission wasn't granted, first grant the permission, then enable Push, then navigate to the Alarms & reminders screen from the system's App info screen and revoke the permission. Then go to Settings → [Account] → Fetching mail → Push folders again.

Closes #7363

[cketti]

I've updated the PR description with some instructions for testing.

[cketti]

I've updated the PR to…

• add previews,
• make the Column scrollable so the content works on small screens,
• inherit from K9Activity so using the in-app language switcher works (testing this requires adding translated strings).