Introduce Parcelable data class to encapsulate the parcelable data

Moving the data that are able to be saved into the Parcelable classes
, so that it can saved and restore from the system.

Since the saved state only keeps the limited information, the
state restoration will be done by reconstructing the state from
the parcelable states.

This is the initial CL to backup some fundamental information.
The later CLs will save more information when needed.

Bug: 289875940
Test: wm presubmit
Flag: com.android.window.flags.ae_back_stack_restore

Change-Id: I05df4b98cc830146455a45239df9d72c7f347f3c