Pass current key to resolveKeyMap method.

Implementations of this method need more context to know if a mapping
should be allowed or forbidden. This is needed for dynamic states like
counts where we don't know at the start how many digits will
follow.

Work for #452.
Convert keymap name return values to KeyMapInfo

Added a new type KeyMapInfo which holds the active key map name and
the current group name (operator, count, register, ...) which triggered
the active key map.

Thanks to this KeyMapResolver can detect if a keystroke is allowed to
trigger a mapping or not when we are in a dynamic group of which the
length is not known at compile time. Take for example counts where we
don't know if the user will type 1, 2 or more digits; the first digit
could also be a trigger for a mapping but the second digit should be
passed straight to the active EditorMode.

Work for #452.
Add test for remapping 0.

Make sure that the actual usecase in #4xx is continuously tested by
means of a unit test.

Fix #452.