[v2::tauri_plugin_positioner] Fix window positioning relative to tray icon

[pronebird]

Hi,

I suppose that event.{x, y} received with TrayIconEvent corresponds to the mouse click position on screen, so if we want to position the window relative to the tray item, then we should rely on icon_rect.{left, top} instead.

It's worth to note that when positioning for TrayBottomCenter the y coordinate for window must be pinned to icon_rect.bottom but that doesn't work because icon_rect has invalid coordinates to begin with, for example:

icon_rect: Rectangle {
  left: 2364.0,
  top: 48.0,
  right: 2422.0,
  bottom: 96.0,
},

I suppose that the tray icon should actually have a top coordinate set to 0 and with the height of 22, double it on my retina and it comes down to:

{
  top: 0,
  bottom: 48.0
}

Which means that icon_rect.top corresponds to the bottom of menubar on macOS.

So unless there is some funny business going on in AppKit, which is possible but unlikely, I'd say that the layer that converts menubar icon frame to screen coordinates on macOS has a bug, so that's something to look into down the road.