Convert rust_libraries and rust_stdlinkage mutators to TransitionMutators

Replace rust.LibraryMutator and rust.LibstdMutator with
TransitionMutators.

Bug: 319288033
Flag: EXEMPT refactor
Test: all soong tests pass
Test: no change to build.ninja
Change-Id: Ia24a582119d39889279d7b93bac9259685153619

androidmk/parser/parser_test.go

@@ -86,20 +86,19 @@ endif`,
 	},
 	{
 		name: "Blank line in rule's command",
-		in:   `all:
+		in: `all:
 	echo first line
 
 	echo second line`,
 		out: []Node{
 			&Rule{
-				Target: SimpleMakeString("all", NoPos),
-				RecipePos: NoPos,
-				Recipe: "echo first line\necho second line",
+				Target:        SimpleMakeString("all", NoPos),
+				RecipePos:     NoPos,
+				Recipe:        "echo first line\necho second line",
 				Prerequisites: SimpleMakeString("", NoPos),
 			},
 		},
 	},
-
 }
 
 func TestParse(t *testing.T) {