Use one mutator for all bp2build conversion.

Each conversion required defining a separate mutator, which will each
operate on _all_ modules and requires each to repeat checks whether the
mutator should operator. Instead, we introduce a single mutator and
modules can define a ConvertWithBp2build to implement bp2build
conversion for that module.

Test: bp2build.sh
Bug: 183079158
Change-Id: I99d4b51f441c2903879092c5b56313d606d4338d

android/filegroup.go

@@ -22,7 +22,6 @@ import (
 
 func init() {
 	RegisterModuleType("filegroup", FileGroupFactory)
-	RegisterBp2BuildMutator("filegroup", FilegroupBp2Build)
 }
 
 var PrepareForTestWithFilegroup = FixtureRegisterWithContext(func(ctx RegistrationContext) {
@@ -34,12 +33,8 @@ type bazelFilegroupAttributes struct {
 	Srcs bazel.LabelListAttribute
 }
 
-func FilegroupBp2Build(ctx TopDownMutatorContext) {
-	fg, ok := ctx.Module().(*fileGroup)
-	if !ok || !fg.ConvertWithBp2build(ctx) {
-		return
-	}
-
+// ConvertWithBp2build performs bp2build conversion of filegroup
+func (fg *fileGroup) ConvertWithBp2build(ctx TopDownMutatorContext) {
 	srcs := bazel.MakeLabelListAttribute(
 		BazelLabelForModuleSrcExcludes(ctx, fg.properties.Srcs, fg.properties.Exclude_srcs))