Split parcelable .aidl files to aidl-export

The one-line "parcelable X" files need to be imported by targets that do
not build against SDK (the SDK has prebuilt definitions), so prepare a
dedicated directory for them.
This avoids having users of the classes include the whole src/
directory, which could contain definitions for classes that are not part
of the public API, so should not be imported.

Also move back to frameworks/base/core some .aidl definitions that
were separated from their associated class.

Bug: 171540887
Test: m
Change-Id: I7432fe4c87cd3cab04dcb6185c9a4f3f84376549