Readd 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, b/308849337, b/309477343
Test: manual
Change-Id: Ic0551990864bba6d03b6bf49fcfd4ae2523d9c6d