Improve error message for which(fn, types)

Error messages for `MethodError` are much more helpful
in determining why the method was not successfully dispatched
than simply "No unique matching method found."

Fixes #47322

base/reflection.jl

@@ -1505,7 +1505,12 @@ See also: [`parentmodule`](@ref), and `@which` and `@edit` in [`InteractiveUtils
 function which(@nospecialize(f), @nospecialize(t))
     t = to_tuple_type(t)
     tt = signature_type(f, t)
-    return which(tt)
+    world = get_world_counter()
+    match, _ = Core.Compiler._findsup(tt, nothing, world)
+    if match === nothing
+        throw(MethodError(f, t, world))
+    end
+    return match.method
 end
 
 """