Add coordinates relative to the current output in i3bar click events

Currently i3bar click events provide x and y coordinates relative to all monitors.
I've added coordinates relative to the current output.

+-----------+-----------+
|           |   i3bar   |
|           +-----------+
|   HDMI-0  |    DP-0   |
| 1920x1080 | 2560x1080 |
+-----------+-----------+

When you click in the top right corner of the DP-0,
i3bar will provide something like this:

{
  "x": 4480,
  "y": 10,
  "output_x": 2560,
  "output_y": 10,
}

This is useful for creating a rofi menu or something else.
rofi -show run -location 1 -xoffset ${I3_OUTPUT_X} -yoffset ${I3_OUTPUT_Y}

RELEASE-NOTES-next

@@ -28,6 +28,7 @@ working. Please reach out to us in that case!
   • mention rofi in default config file
   • i3-input: add different exit codes for when i3-input fails
   • allow ppt values in move direction and move position commands
+  • i3bar: add coordinates relative to the current output in i3bar click events
 
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  │ Bugfixes                   │