Make Core.TypeofUnion use the type method table (#55188)

Ensures that adding or examining the methods of Type{Union{}} in the
method table returns the correct results.

Fixes #55187

(cherry picked from commit d68befd)

src/jltypes.c

@@ -3518,8 +3518,11 @@ void jl_init_types(void) JL_GC_DISABLED
                                        jl_emptysvec, 0, 0, 4);
 
     // all Kinds share the Type method table (not the nonfunction one)
-    jl_unionall_type->name->mt = jl_uniontype_type->name->mt = jl_datatype_type->name->mt =
-        jl_type_type_mt;
+    jl_unionall_type->name->mt =
+        jl_uniontype_type->name->mt =
+        jl_datatype_type->name->mt =
+        jl_typeofbottom_type->name->mt =
+            jl_type_type_mt;
 
     jl_intrinsic_type = jl_new_primitivetype((jl_value_t*)jl_symbol("IntrinsicFunction"), core,
                                              jl_builtin_type, jl_emptysvec, 32);

test/reflection.jl

@@ -1193,3 +1193,5 @@ end
 @test Base.isexported(Mod52812, :b)
 @test Base.ispublic(Mod52812, :a)
 @test Base.ispublic(Mod52812, :b)
+
+@test methods(Union{}) == Any[m.method for m in Base._methods_by_ftype(Tuple{Core.TypeofBottom, Vararg}, 1, Base.get_world_counter())] # issue #55187