refactor bp2build module allowlists into struct

To make testing easier, refactor existing module-global variables into a
struct that can be mocked.

Test: build/bazel/bp2build.go
Change-Id: I9d177677644ea743641a745b1839a3a8b29f902a
diff --git a/android/config.go b/android/config.go
index 5dcb959..cb2fc61 100644
--- a/android/config.go
+++ b/android/config.go
@@ -158,7 +158,7 @@
 	mockBpList string
 
 	runningAsBp2Build              bool
-	bp2buildPackageConfig          Bp2BuildConfig
+	bp2buildPackageConfig          bp2BuildConversionAllowlist
 	Bp2buildSoongConfigDefinitions soongconfig.Bp2BuildSoongConfigDefinitions
 
 	// If testAllowNonExistentPaths is true then PathForSource and PathForModuleSrc won't error
@@ -550,7 +550,7 @@
 	}
 
 	config.BazelContext, err = NewBazelContext(config)
-	config.bp2buildPackageConfig = bp2buildDefaultConfig
+	config.bp2buildPackageConfig = bp2buildAllowlist
 
 	return Config{config}, err
 }