Add support for PRODUCT_RELEASE_CONFIG_MAPS

This allows product config to determine what build flags are present in
a product's build, as well as their value.

As product config moves to a declarative specification, this can be
handled with less unnecessary work.

Bug: b/302593603
Bug: b/308849337
Test: manual
Change-Id: If57622059bb7d1c33df7498321db621c0c2d30c0