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
diff --git a/core/soong_config.mk b/core/soong_config.mk
index 88a210a..53a1064 100644
--- a/core/soong_config.mk
+++ b/core/soong_config.mk
@@ -40,6 +40,7 @@
 $(call add_json_str,  Platform_base_os,                  $(PLATFORM_BASE_OS))
 $(call add_json_str,  Platform_version_last_stable,      $(PLATFORM_VERSION_LAST_STABLE))
 $(call add_json_str,  Platform_version_known_codenames,  $(PLATFORM_VERSION_KNOWN_CODENAMES))
+$(call add_json_bool, Release_aidl_use_unfrozen,         $(RELEASE_AIDL_USE_UNFROZEN))
 
 $(call add_json_str,  Platform_min_supported_target_sdk_version, $(PLATFORM_MIN_SUPPORTED_TARGET_SDK_VERSION))