[Feature Request] key-holding

I love this emulator so much but there's been stuff that's troubling sense I'm trying to figure out what to do with the Windows XP VM

**Key-Holding:**

I think what would be useful for the people who actually got games working on UTM that don't need GPU acceleration to be able to hold keys on a keyboard or able to setup a custom keyboard to easily access keys from top bar like macros in a way. Could have a option to have on screen macros like if it was a controller emulator.

For example if I want to charge my gun in _Worms Armageddon_ I would need to hold space bar but it's currently impossible to do so.

Video Example: https://cdn.discordapp.com/attachments/694255182581858447/776951381588181043/video0.mov

Here's another one that I think should be added that I did a post on. https://github.com/utmapp/UTM/issues/533