Add minTargetSdkVersion input selector to libselinux

Motivation:
Provide the ability to phase in new security policies by
applying them to apps with a minimum targetSdkVersion

Test: Marlin builds and boots. Apps targeting targetSdkVersion<=25
run in untrusted_app_25 domain. Apps targeting the current development
build >=26 run in the untrusted_app domain with fewer permissions. No
new denials observed during testing.
Bug: 34115651
Change-Id: Ieed0d19a93cc2d4a8a3f0b434f79933c53a6d0b4
1 file changed