feat: add buffer-close-right and buffer-close-left commands

[atomicptr]

Adds the ability to close buffers left and right of the current one. I find myself very often to close multiple buffers at once but buffer-close-other and buffer-close-all often tend to close too much so I'm often closing buffers one by one which can be a bit cumbersome at task. Editors like VS Code (and others) usually have a "Close tabs to the right/left" option when you right click a tab and since switching I wanted to have this in Helix too.