Bind commands to `event.keyCode` instead of letters

[InvisibleRain]

The issue is already reported or known issue?

• [X] I have searched the existing issues on github
• [X] I am using the latest version

Description

Keymaps don't work when using a non-English keyboard layout (e.g. Russian). A dirty workaround is to duplicate all the keymaps in the config and replace the English letters with letters of another language. Another way to fix this, would be to use KeyboardEvent.code instead of KeyboardEvent.key in InputDriver.ts

This is a feature request instead of a bug report because, despite improving UX for most users, such a change may break existing installations for AZERTY or QWERTZ users. So, the best way would be to make this feature optional under the properties section.

Other details

Users asking for the feature: https://github.com/ueokande/vim-vixen/issues/1442