Support "in-memory" ZenMode

For the "add a mode" flow we need to create and edit a ZenMode instance without writing it to the backend until the user confirms. Therefore, we now support:
* parceling a ZenMode (so it can be restored in onSaveInstanceState/onCreate).
* creating a custom_manual ZenMode instance without interacting with NMS/ZenModeBackend.

Bug: 326442408
Test: atest com.android.settingslib.notification.modes.ZenModeTest
Flag: android.app.modes_ui
Change-Id: Ie502175a91c5148ef156a7236feb6120d42d220d