AAPT2: Share split functionality between link and optimize

Generating splits should be possible to do from the optimize command.
This means that a lot of infrastructure around split APKs can be
shared by both the optimize and link phase.

Bug: 35925830
Change-Id: Ia88b9e4bff300a56353b2f7a4a2547c8eb43a299
Test: manual
25 files changed