New layout: symmetrical tall (for ultrawide screens)

[totoroot]

Describe your request

Similar to issue #22 I would like to have an additional layout for my ultrawide screen, where the main column is in the center and remaining windows get arranged symmetrically to the left and right.

Since I'm quite familiar with the code base I will probably tackle this myself, but wanted to open an issue, so others looking for something similar can find it and so I can track my progress when working on this.

It would probably make sense to create two separate layouts which prioritise left or right, when opening new windows, so that it's similar to layouts tall and rtall but with symmetrical distribution.

Briefly explain its use-case

Example visualisation for suggested symmetrical layout with priorisation left (analog to rtall):

First window
 ______________________
|                      |
|                      |
|                      |
|______________________|

Second window
 ______________________
|   |                  |
|   |                  |
|   |                  |
|___|__________________|

Third window
 ______________________
|   |              |   |
|   |              |   |
|   |              |   |
|___|______________|___|

Fourth window
 ______________________
|   |              |   |
|___|              |   |
|   |              |   |
|___|______________|___|

Fifth window
 ______________________
|   |              |   |
|___|              |___|
|   |              |   |
|___|______________|___|

[phenax]

Closing this as duplicate of #1. Had run into some challenges implementing this back in the day but might be worth re-visiting. Feel free to carry over any discussions over there.