Feature: Better position semantics on ui functions

[Sxmourai]

I think the position parameters for ui functions on macroquad::ui::Ui should be changed because using Option is quite misleading.
A better idea should be with an enum kind of like this:

enum Position {
  Auto,
  Absolute(Vec2), // Previous position type
  // We can now add other position types like
  // Percent(f32), (like bevy)
  // ...
}