Merge changes from topic "system_build_prop_soong" into main

* changes:
  Use Soong-built system/build.prop
  Sync gen_build_prop.py to sysprop.mk
  Add TARGET_SYSTEM_PROP to system build.prop

android/config.go

@@ -2077,3 +2077,7 @@ func (c *config) UseDebugArt() bool {
 
 	return Bool(c.productVariables.Eng)
 }
+
+func (c *config) SystemPropFiles(ctx PathContext) Paths {
+	return PathsForSource(ctx, c.productVariables.SystemPropFiles)
+}