Fix java prebuilts

The java prebuilt tests weren't registering the prebuilts mutators,
which hid an issue where prebuilts modules weren't getting renamed
to avoid collisions with source modules of the same name, which
ended up causing the prebuilt module to try to add a dependency
on itself.

Test: java_test.go
Change-Id: I3327d27533591cb08a4b8b8b5e1668a6f72be8df

java/java.go

@@ -531,6 +531,10 @@ func (j *Prebuilt) Prebuilt() *android.Prebuilt {
 	return &j.prebuilt
 }
 
+func (j *Prebuilt) Name() string {
+	return j.prebuilt.Name(j.ModuleBase.Name())
+}
+
 func (j *Prebuilt) DepsMutator(ctx android.BottomUpMutatorContext) {
 }