Make Magikeyboard work under Samsung Dex (like it was done for KeePassDX in #1114)

[pawel-smth]

Is your feature request related to a problem? Please describe.
Though KeePassDX app itself was "enabled" to work with Samsung Dex (fix/merge #1114 addressed #245 #537 #963), it looks like Magikeyboard is not yet fully supported/updated to work under Dex
Sympthoms:

1. Magikeyboard is not listed in phone's settings where one enables/disables installed keyboards.
2. Magikeyboard is not listed on "Choose input method" Android pop-up when to press "keyboard selection" key of gboard/samsung keyboard
3. "Activate a custom keyboard ..." info is displayed under "Form filling" setting of KeePassDX app
4. If to exit Dex mode, Magikeyboard becomes visible in KB selection and works as expected.

Describe the solution you'd like
Update Magikeyboard to work under Samsung Dex

Describe alternatives you've considered
Obvious one is not to use Magikeyboard and just use copy-paste via clipboards, but it's less safe than via MK and obviously less user-friendly.

Additional context
Screenshots - attached (one with MK visible was done in non-dex mode).
I've tried to change where the keyboard is displayed in Dex mode (either on external monitor/display or on the phone), but it doesn't matter - MK is not listed.