Test: Find in terminal

[Tyriar]

Test for #15198

Complexity: 2

• Linux - @mjbvz
• macOS - @egamma
• Windows - @gregvanl

The terminal now features a find widget which can be accessed via ctrl+f or cmd+f if the terminal is focused. It should work very similar to the editor find widget just with less capabilities and tuned for use in the terminal.

Find next/previous will search either from the top row of the viewport, or from the selection if there is one. Note that the regular selection is used to present the search result, not a special "find selection" like in the editor.

See known issues/improvements in #28768