Allow double press shortcuts with modifier keys

**Is your feature request related to a problem? Please describe.**

I want to search menus quickly. I am used to pressing Shift+Shift in IDEA and others to search menus.

**Describe the solution you'd like**

allow double press shortcuts with modifier keys:

- Shift+Shift
- Ctrl+Ctrl
- Mod4+Mod4 (Super+Super)
- Alt+Alt

**Describe alternatives you've considered**

using a "normal" keyboard shortcut. Shift+Shift is hardcoded to my brain by now

**Additional context**

modifier-only (and modifiers combo) shortcuts are currently not allowed at all