Add min_sdk_version property to apexes

Add a min_sdk_version property apexes.  Currently a noop, but will
be used to enforce that dependencies are compatible with the
specified version.

Test: m checkbuild
Bug: 149591522
Merged-In: I923773c90fe15becbffae3986791aa9edde8f8f6
Change-Id: I923773c90fe15becbffae3986791aa9edde8f8f6
(cherry picked from commit 50317874)