Add new Release_aidl_use_unfrozen soong variable

This comes from a trunk stable build flag `RELEASE_AIDL_USE_UNFROZEN`
and is used by the AIDL compiler when creating build rules for the
generated AIDL libraries.

Test: m
Bug: 290265210

Change-Id: I9161a3262d6b2ef8792e8c0b8a759da9a540c560