Add a new CreateSoongInjectionDirFiles function

- This is a wrapper function for all files in soong_injection directory.
This should prevent an error in the workspace generated for
api_bp2build.
- Rename the existing CreateSoongInjectionFiles fn and make it package
  private to prevent confusion

(The subsequent CL in this stack should contain a smoke test for
api_bp2build)

Test: b build //:empty --config=api_bp2build --config=android
Test: TH
Change-Id: Iddb0aa1aff2f709826edd587aa99fccddf80f08f
diff --git a/bp2build/bp2build.go b/bp2build/bp2build.go
index 5dc9612..86b9b27 100644
--- a/bp2build/bp2build.go
+++ b/bp2build/bp2build.go
@@ -45,17 +45,27 @@
 	bp2buildFiles := CreateBazelFiles(ctx.Config(), nil, res.buildFileToTargets, ctx.mode)
 	writeFiles(ctx, bp2buildDir, bp2buildFiles)
 
+	soongInjectionDir := android.PathForOutput(ctx, bazel.SoongInjectionDirName)
+	writeFiles(ctx, soongInjectionDir, CreateSoongInjectionDirFiles(ctx, res.metrics))
+
+	return &res.metrics
+}
+
+// Wrapper function that will be responsible for all files in soong_injection directory
+// This includes
+// 1. config value(s) that are hardcoded in Soong
+// 2. product_config variables
+func CreateSoongInjectionDirFiles(ctx *CodegenContext, metrics CodegenMetrics) []BazelFile {
+	var ret []BazelFile
+
 	productConfigFiles, err := CreateProductConfigFiles(ctx)
 	if err != nil {
 		fmt.Printf("ERROR: %s", err.Error())
 		os.Exit(1)
 	}
-
-	soongInjectionDir := android.PathForOutput(ctx, bazel.SoongInjectionDirName)
-	writeFiles(ctx, soongInjectionDir, productConfigFiles)
-	writeFiles(ctx, soongInjectionDir, CreateSoongInjectionFiles(ctx.Config(), res.metrics))
-
-	return &res.metrics
+	ret = append(ret, productConfigFiles...)
+	ret = append(ret, soongInjectionFiles(ctx.Config(), metrics)...)
+	return ret
 }
 
 // Get the output directory and create it if it doesn't exist.