Move activity finish methods to ActivityRecord

Methods dedicated to finishing activities in ActivityStack mostly
operate with internal ActivityRecord state and call ActivityRecord
methods, so it makes sense to move them there.

No change in functionality, only code being moved around.

Bug: 137329632
Test: Build and flash
Change-Id: Ic3555c3279a5e918925fc4bae3a4d2fa6b35fd74
9 files changed