Add a prod var to override package names.

Currently only java/app.go is affected by package name overrides. When
the var is used, the corresponding module's install APK name is changed
to the overriding name.

Bug: 122957760
Test: app_test.go + TreeHugger
Change-Id: Ie522da3d7280970d740d779cf2694560feae6180

android/config.go

@@ -918,6 +918,17 @@ func (c *deviceConfig) OverrideCertificateFor(name string) (certificatePath stri
 		"invalid override rule %q in PRODUCT_CERTIFICATE_OVERRIDES should be <module_name>:<certificate_module_name>")
 }
 
+func (c *deviceConfig) OverridePackageNameFor(name string) string {
+	newName, overridden := findOverrideValue(
+		c.config.productVariables.PackageNameOverrides,
+		name,
+		"invalid override rule %q in PRODUCT_PACKAGE_NAME_OVERRIDES should be <module_name>:<package_name>")
+	if overridden {
+		return newName
+	}
+	return name
+}
+
 func findOverrideValue(overrides []string, name string, errorMsg string) (newValue string, overridden bool) {
 	if overrides == nil || len(overrides) == 0 {
 		return "", false