Simulated directional modifier

`skhd -k` only works for the "neutral" modifier keys: "cmd, ctrl, ...". The directional modifier keys "lcmd, rcmd, ..." are ignored and the key is pressed without any modifiers.

Proposed solution:
- Neutral modifiers send left modifier (as it is right now)
- Directional modifiers send appropriate modifier

Currently you cannot simulate a keypress "rctrl - a"

Start at the `skhd -k` command path and trace how neutral and directional modifier names are handled. Verify the behavior for `rctrl - a` and related left/right modifiers; done means neutral modifiers retain their current behavior while directional modifiers apply the corresponding side-specific modifier.

Written by the indexing model from the issue text.