Expose ability to set level from uid.

Extract the existing level computation into a helper function.

Add selinux_android_context_with_level() to take a context string and
return a new one with appropriate level based on user and/or app id.

Test: builds
Bug: 141677108
Change-Id: I4618d4c74d1a2b94de9e934a8caf2e24049f0477
3 files changed