Allow apex dependencies to be restricted to source modules only

An upcoming change to create a prebuilt_platform_compat_config module
will break if the apex tries to use it instead of a
platform_compat_config because the former does not provide all the
information that the apex needs. This change will allow the
compatConfigsTag to be configured to prevent the prebuilt from being
used even when it is preferred.

Bug: 182402754
Test: m nothing
Change-Id: Ib9dc06c038f7cf3fc229f3c4d2b025335a4715b4