feat: new statusline.merge-with-commandline option

[NikitaRevenco]

Having the command line and the statusline each take 2 rows may not be desirable to all.

Kakoune and Neovim both offer the option to merge these two lines into a single line.

The biggest problem is that since the status message is almost always empty, it takes up an entire line at the bottom of the screen which could be used by actual text instead.

I added a config option that merges the statusline and the command line into a single one. if there is an editor message, it replaces the bottom command line.

---

To enable it, run :toggle statusline.merge-with-commandline or add this into config.toml:

[editor.statusline]
merge-with-commandline: true

Before vs After

Before

After

Supersedes #12020
Closes #7934

[rockboynton]

This made me think; what about swapping the command line and status line, and having the command line be "transparent" to the buffer/window by default? Then if you start typing a command, it pops up above the status line? Seems like the best of both worlds since you would still be able to see the status line when typing a command

[NikitaRevenco]

This made me think; what about swapping the command line and status line, and having the command line be "transparent" to the buffer/window by default? Then if you start typing a command, it pops up above the status line? Seems like the best of both worlds since you would still be able to see the status line when typing a command

I think there's still value in having 1 line vs 2 lines at the bottom. I agree swapping them would be a better default (out of scope of this PR), but imo there should still be an option to merge them for those who want it