Move XML object factory logic to libcore

It makes sense to hide the details of the parser implementation
(and other similar objects) in libcore so that framework code is
isolated from implementation choices.

Test: build
Bug: 111055375
Merged-In: I88548c991178c0a2971f6e2b99216b5a6aae0b09
Change-Id: I88548c991178c0a2971f6e2b99216b5a6aae0b09