bp2build: refactor BazelTargetModule naming boilerplate.

This CL replaces the "__bp2build__" name prefix boilerplate with a props
creation function, and centralizes the prefixing in there.

Test: TH
Test: soong tests
Change-Id: Ic963199ab60dcce0d3361abff111cfa9acd4c21b
diff --git a/genrule/genrule.go b/genrule/genrule.go
index a500c27..9fa6c48 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -853,12 +853,7 @@
 		Tools: tools,
 	}
 
-	// Can we automate this?
-	name := "__bp2build__" + m.Name()
-	props := bazel.BazelTargetModuleProperties{
-		Name:       &name,
-		Rule_class: "genrule",
-	}
+	props := bazel.NewBazelTargetModuleProperties(m.Name(), "genrule", "")
 
 	// Create the BazelTargetModule.
 	ctx.CreateBazelTargetModule(BazelGenruleFactory, props, attrs)