Convert AFDO mutators to TransitionMutator

Convert afdoDepsMutator and afdoMutator to a TransitionMutator as a
step towards variants-on-demand.

This relands Ib05845455ccf43a07b3915a0d7b0a95896062f13 with a fix
to maintain the current behavior of not using AFDO variants for
dependencies of the linker static binary.

Bug: 319288033
Bug: 324141705
Test: afdo_test.go
Change-Id: I76e30021173fc5b7e9e1fa826039776eb3dc7b6e

rust/afdo.go

@@ -44,14 +44,14 @@ func (afdo *afdo) addDep(ctx BaseModuleContext, actx android.BottomUpMutatorCont
 		if err != nil {
 			ctx.ModuleErrorf("%s", err.Error())
 		}
-		if fdoProfileName != nil {
+		if fdoProfileName != "" {
 			actx.AddFarVariationDependencies(
 				[]blueprint.Variation{
 					{Mutator: "arch", Variation: actx.Target().ArchVariation()},
 					{Mutator: "os", Variation: "android"},
 				},
 				cc.FdoProfileTag,
-				[]string{*fdoProfileName}...,
+				[]string{fdoProfileName}...,
 			)
 		}
 	}