untrusted_app: policy versioning based on targetSdkVersion

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

Place untrusted apps with targetSdkVersion<=25 into the
untrustd_app_25 domain. Apps with targetSdkVersion>=26 are placed
into the untrusted_app domain. Common rules are included in the
untrusted_app_all attribute. Apps with a more recent targetSdkVersion
are granted fewer permissions.

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
Bug: 35323421
Change-Id: Ie6a015566fac07c44ea06c963c40793fcdc9a083