Move ShortcutsTutorial as a standalone DialogFragment

Using a standalone DialogFragment is more flexible if we ever want to
store the UI state in onSaveInstance during fragment lifecycle.

What this cl includes:
- Move shortcuts tutorial into DialogFragment
- Clean up the dialog button click listener. We always dismiss the
  dialog
- Clean up code path that are obsolete
- Refactor the ToggleAccessibilityServicePreferenceFragmentTest

Bug:406052931
Test: Manual Clicking on the shorcut toggles on accessibility feature
screens and verify the tutorial shows up as expected
Test: atest com.android.settings.accessibility
Flag: EXEMPT refactor that won't be cleaner with feature flag

Change-Id: I944c79a1f6cee75b7bd9ecdcdd27b6faa7bd91cf