Refactoring Accessibility settings to use ShortcutConstants.UserShortcutType

This removes AccessibilityUtil.UserShortcutType,
replacing all mention of it with ShortcutConstants.UserShortcutType

NO_IFTTT=UI order not changed
Test: atest com.android.settings.accessibility
Bug: 322014084
Flag: EXEMPT internal refactoring

Change-Id: I18695d040c4bd08a455143594e770adda2b1a8de