add a module-level allowlist to bp2build

We currently enabled modules in bp2build on a package level, and we
disable individual modules based on a denylist. To enable a specific
module individually, we must change the corresponding Android.bp file to
include a bp2build_available property. Instead, have a centralized list
of specifically enabled modules.

Bug: 220875679
Test: m bp2build
Change-Id: I908f2f2366b72affb04234fbe92ba03bf5a37338