add module type allowlist to bp2build

This change also requires that java_import modules be prepended with the
"prebuilt_" prefix in the `bp2buildModuleAlwaysConvertList`. This fixes
a bug where trying to disable a java_import by name without the
"prebuilt_" prefix would also disable the corresponding source module if
it exists with the same name.

Test: build/bazel/ci/bp2build.sh
Change-Id: If75236891810e5112d70441653be4644d8fe5ecf