Adds Vim-Like Scrolling to XPLR

[ElSamhaa]

• Added through a setting vimlike_scrolling which is turned off by default
• A hard-coded (for now) cushion of 5 lines that allows for previewing the next lines while scrolling
• A separate struct ScrollState with getters and setters for the current_focus field to disallow setting the field without updating the last_focus field

[sayanarijit]

Wow… thanks for pr. I’ll review soon.

[ElSamhaa]

• An initial cushion value is now set to 5. The cushion value is now dynamically set to accommodate small view ports (table heights).

[sayanarijit]

I wanted to avoid mutable state in UI code, but looks like it's worth the tradeoff.