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

android/bazel_paths.go

@@ -79,6 +79,7 @@ type BazelConversionContext interface {
 	OtherModuleType(m blueprint.Module) string
 	OtherModuleName(m blueprint.Module) string
 	OtherModuleDir(m blueprint.Module) string
+	ModuleErrorf(format string, args ...interface{})
 }
 
 // A subset of the ModuleContext methods which are sufficient to resolve references to paths/deps in