Add support for auto-generated characteristics RRO

Setting Generate_product_characteristics_rro will automatically generate
an RRO package which contains resources with
'product="{PRODUCT_CHARACTERISTICS}"'. The RRO package will be installed
to /product partition. The app will be compiled with '--product
default', making the app identical to all targets.

Motivation for this change is to minimize divergence of system.img.

Bug: 294799593
Test: boot and idmap2 dump
Change-Id: I1371f7410a1ecf337e1f73214b024af39aa6d57a
diff --git a/java/androidmk.go b/java/androidmk.go
index 97b303d..84f78c8 100644
--- a/java/androidmk.go
+++ b/java/androidmk.go
@@ -343,10 +343,15 @@
 			Disabled: true,
 		}}
 	}
+	var required []string
+	if proptools.Bool(app.appProperties.Generate_product_characteristics_rro) {
+		required = []string{app.productCharacteristicsRROPackageName()}
+	}
 	return []android.AndroidMkEntries{android.AndroidMkEntries{
 		Class:      "APPS",
 		OutputFile: android.OptionalPathForPath(app.outputFile),
 		Include:    "$(BUILD_SYSTEM)/soong_app_prebuilt.mk",
+		Required:   required,
 		ExtraEntries: []android.AndroidMkExtraEntriesFunc{
 			func(ctx android.AndroidMkExtraEntriesContext, entries *android.AndroidMkEntries) {
 				// App module names can be overridden.