Support more keyboard layouts: colemak, dvorak, workman, neo, ...?

### Describe your request

The `:input layout` module already has `+azerty` and `+bepo`, but there's interest in supporting other layouts:

- https://github.com/doomemacs/core/issues/767
- https://github.com/doomemacs/core/issues/783
- https://github.com/doomemacs/core/issues/2018
- https://github.com/doomemacs/core/issues/2722

This issue combines these requests into one. Unfortunately, I'm a basic QWERTY boi with no plans to switch, so my ability to assess good rebindings is limited, so PRs are not only welcome, they are needed!

### Layouts

- [ ] Colemak
- [ ] Dvorak
- [ ] Workman
- [ ] Neo

### Notes

- Layout support should be gated behind the appropriate flag (e.g. `+dvorak`, `+colemak`, etc), and loaded from `+layout-init-h` in `input/layout/config.el`.
- A general and/or simpler solution is preferred (perhaps something like [Spacemacs' keyboard-layout layer](https://github.com/syl20bnr/spacemacs/tree/master/layers/%2Bintl/keyboard-layout). I welcome attempts to rewrite the module, if you're motivated to do so.
- Rebinding all of Doom's keys after-the-fact should be a last resort, but is acceptable as an intermediate.
- Even if your PR isn't used as is, it can still be a helpful reference for me to base a final implementation on.
- I suggest you wait for Doom v3. I'm phasing out `general` and introducing new keymaps for many of Doom's global default keys (including leader/localleader keys), both of which will impact this module (and the latter may give a general solution something to target when swapping keys).