PackageInfo: add Parcel read/write for cert history.

commit: 5cdda342 added a new flag,
GET_SIGNING_CERTIFICATES to PackageManager for use with getPackageInfo
that returns the signing certificate history, including the current signer,
of the given package.  This is intended to replace the existing
GET_SIGNATURES flag and corresponding field.  The previous commit did not,
however, implement the read/write Parcelable methods so that this
information could be reconstructed client side.  Implement those methods
to actually expose the new API.

Bug: 64686581
Test: Test app pull of PackageInfo with GET_SIGNING_CERTIFICATES succeeds.
Change-Id: I1c023da2a6fd03e11432953080045a79b9f56839