Add context for ro.product.property_source_order

Any partitions should be able to write this property with build.prop.
This adds a new context for ro.product.property_source_order so it can
be set from any build.prop, e.g. vendor/build.prop, product/build.prop,
etc.

Bug: 172459064
Test: PRODUCT_VENDOR_PROPERTIES can set this property
Change-Id: Ibf85a4ad02d8454f621428b271e8e298067aa126
diff --git a/private/compat/30.0/30.0.cil b/private/compat/30.0/30.0.cil
index 592a1f9..9cc23b4 100644
--- a/private/compat/30.0/30.0.cil
+++ b/private/compat/30.0/30.0.cil
@@ -1299,6 +1299,7 @@
 (typeattributeset default_android_vndservice_30_0 (default_android_vndservice))
 (typeattributeset default_prop_30_0 (
     default_prop
+    build_config_prop
     init_service_status_private_prop
     setupwizard_prop
     verity_status_prop