Enforce supported container for mainline beta namespaces

For mainline beta namespaces, only platform container or the
corresponding mainline module container are supported. If a mainline
module A tries to create a flag in module B's namespace, the build
should fail.

Bug: b/406508083
Test: atest -c
Change-Id: I7ad0db1195e095952f06ba5680f57ac08cd6e90a