Autogenerate a vendor-build.prop for the current product

The autogenerated soong vendor.img will use the autogenerated soong
vendor-build.prop module. The autogenerated vendor-build.prop module is
missing support for `android-info.txt` which is an additional input as
--prop-files. Support for that will be added in a followup CL.

Test: verified that autogenerated vendor.img for aosp_cf_x86_64_phone
contains a build.prop file, and its contents are equivalent to kati
built vendor build.prop file

Bug: 375500423
Change-Id: I46b3c2e7cf44300820dcd2f7a9799ad11730691e
diff --git a/android/build_prop.go b/android/build_prop.go
index 120ad94..7c3c506 100644
--- a/android/build_prop.go
+++ b/android/build_prop.go
@@ -20,7 +20,7 @@
 
 func init() {
 	ctx := InitRegistrationContext
-	ctx.RegisterModuleType("build_prop", buildPropFactory)
+	ctx.RegisterModuleType("build_prop", BuildPropFactory)
 }
 
 type buildPropProperties struct {
@@ -191,7 +191,7 @@
 // build_prop module generates {partition}/build.prop file. At first common build properties are
 // printed based on Soong config variables. And then prop_files are printed as-is. Finally,
 // post_process_props tool is run to check if the result build.prop is valid or not.
-func buildPropFactory() Module {
+func BuildPropFactory() Module {
 	module := &buildPropModule{}
 	module.AddProperties(&module.properties)
 	InitAndroidArchModule(module, DeviceSupported, MultilibCommon)