Highlight terminal commands subtly when mousing over them

[Tyriar]

Highlighting a block would give the user a hint when hovering the terminal that it knows a lot more than a regular terminal. For example this part could be slightly darker or lighter depending on the theme:

[Tyriar]

This needs xtermjs/xterm.js#4855 and probably another API that forces the decoration to render on non-null cells

[Tyriar]

Another idea is to extends the solid bar on the left when hovering, right clicking could bring up the command's SI menu

[Tyriar]

I got a basic version of this working and it looked out of place:

Instead of background color I tried the re-use the command navigation focus bar on the left and it felt too noisy, especially when you compare it to what the editor looks like when you hover it.

Prototype: #198219

I started a discussion with the team