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: I94445c870ac908474e62db0b3172b64d53680852