Let Release_aidl_use_unfrozen add vintf_fragments

The product_config variable can be used to add different
vintf_fragments.

Ignore-AOSP-First: this is required for vFRC finalization and needs to be submitted ASAP. This can be cherry-picked to aosp after finalization.

Test: launch_cvd && atest hal_implementation_test
Test: lunch `next` && atest vts_treble_vintf_framework_test
Bug: 279809333
Change-Id: Ied17ad4c4564a5d97f93001734fba7cc6648bbc2

android/variable.go

@@ -183,6 +183,7 @@ type variableProperties struct {
 		Release_aidl_use_unfrozen struct {
 			Cflags          []string
 			Cmd             *string
+			Vintf_fragments []string
 		}
 	} `android:"arch_variant"`
 }