Expose 'ParcelableHolder' as SystemApi

ParcelableHolder is the way to extend already defined parcelables. So,
it's supposed to be used by OEM's modules.

For Parcelable to be used by the OEM's module, it should be exposed as
SystemApi

Bug: 146611855
Test: atest aidl_unittests aidl_integration_test CtsNdkBinderTest
Change-Id: I3d3e3d6b22ffd128dcfc8281d998ee3f55a398c5