Add copy ctor for ParcelableHolder

For the parity with other parcelable, make ParcelableHolder copyable, so
that a parcelable which contains ParcelableHolder can be copyable.

Bug: 209872866
Bug: 210093811
Test: declare a parcelable array which contains ParcelableHolder and
then check if build succeeds

Change-Id: I80c2c544f12c5ace261612b35a1aa187bfe96214