Have ConvertWBp2build use Bp2buildMutatorContext

This no-op refactoring facilitates some upcoming functional changes for
"bp2build allowlist v2". The work requires that the bp2build conversion
mutator be changed from a TopDown mutator to a BottomUp mutator.
Refactoring all bp2build-related methods so that they use Bp2buildMutatorContext
makes it easier to make this functional change without touching tens of
files and multiple projects.

Bug: 285631638
Test: m bp2build
Change-Id: I3d1ef3064146e959c6f0dc315350fc9764bf2bd2
diff --git a/rust/library.go b/rust/library.go
index 3f031c1..0357086 100644
--- a/rust/library.go
+++ b/rust/library.go
@@ -810,7 +810,7 @@
 	Proc_macro_deps bazel.LabelListAttribute
 }
 
-func libraryBp2build(ctx android.TopDownMutatorContext, m *Module) {
+func libraryBp2build(ctx android.Bp2buildMutatorContext, m *Module) {
 	lib := m.compiler.(*libraryDecorator)
 
 	srcs, compileData := srcsAndCompileDataAttrs(ctx, *lib.baseCompiler)
@@ -887,7 +887,7 @@
 	Version bazel.StringAttribute
 }
 
-func cargoBuildScriptBp2build(ctx android.TopDownMutatorContext, m *Module) *string {
+func cargoBuildScriptBp2build(ctx android.Bp2buildMutatorContext, m *Module) *string {
 	// Soong treats some crates like libprotobuf as special in that they have
 	// cargo build script ran to produce an out folder and check it into AOSP
 	// For example, https://cs.android.com/android/platform/superproject/main/+/main:external/rust/crates/protobuf/out/