Add product_config module

product_config module will export productVariables struct (defined in
android/variable.go). Other modules can depend on product_Config module
to read product variables, without needing to update Soong.

Bug: 346214955
Test: build and see output of product_config module
Change-Id: I06e1d2716dc2a8b90984bb46c5fc901cd1ca5020
diff --git a/ui/build/soong.go b/ui/build/soong.go
index 2f3150d..99474d9 100644
--- a/ui/build/soong.go
+++ b/ui/build/soong.go
@@ -694,6 +694,7 @@
 		}
 	}
 	distFile(ctx, config, config.SoongVarsFile(), "soong")
+	distFile(ctx, config, config.SoongExtraVarsFile(), "soong")
 
 	if !config.SkipKati() {
 		distGzipFile(ctx, config, config.SoongAndroidMk(), "soong")