Build product/odm build.prop with Soong

Bug: 322090587
Test: compare build.prop before and after, boot
Change-Id: I7a7dc785030a0c17e5c09b7f65c978fe9bbcb7a7
diff --git a/android/variable.go b/android/variable.go
index c9b29f1..4025607 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -510,6 +510,7 @@
 
 	SystemPropFiles    []string `json:",omitempty"`
 	SystemExtPropFiles []string `json:",omitempty"`
+	ProductPropFiles   []string `json:",omitempty"`
 
 	EnableUffdGc *string `json:",omitempty"`
 }