Soong system image may update the $PRODUCT_OUT

A target must define "USE_SOONG_DEFINED_SYSTEM_IMAGE := true" and
"PRODUCT_SOONG_DEFINED_SYSTEM_IMAGE := <name of soong system image>"
to use the soong defined system image.
The system image must install the files to $PRODUCT_OUT for adb sync
and build verification. Instead of using 'update_product_out'
property in Android.bp, copy the files only if the name of the image
matches with PRODUCT_SOONG_DEFINED_SYSTEM_IMAGE.

Bug: 350599535
Bug: 365700376
Test: lunch aosp_x86_64-trunk_staging-userdebug && m &&
      m aosp_cf_system_x86_64
Test: lunch aosp_cf_x86_64_phone_soong_system-trunk_staging-userdebug
      && m
      and adb sync on the cf device
Change-Id: If8673ba2855a753a5559a588bd83068d950fd7e4

android/variable.go

@@ -423,6 +423,9 @@ type ProductVariables struct {
 
 	TargetFSConfigGen []string `json:",omitempty"`
 
+	UseSoongSystemImage            *bool   `json:",omitempty"`
+	ProductSoongDefinedSystemImage *string `json:",omitempty"`
+
 	EnforceProductPartitionInterface *bool `json:",omitempty"`
 
 	EnforceInterPartitionJavaSdkLibrary *bool    `json:",omitempty"`