Update prebuilts to androidx.test 1.1 beta02.

Also:
 - add a script which automates the drop + bp generation using
pom2bp.
 - add a rule for kxml2 on target
 - move to prebuilts/misc/common for consistency

Test: m -j checkbuild
Change-Id: I6990153f16bdfc77c70c6eec5ded4facc67223af
Merged-In: I300346b7f63260872c1a3c694d8bda16e7c4ac8d