* Refactor: KeyValue constants

Add constants for keys that are accessed from the app's code. This
simplifies the fake pointer handling in Keyboard2View.

* Refactor: Pre-compute action key replacement

The action key and the enter swap are pre-computed in EditorConfig. This
simplifies the code.

The "Switch to the last used keyboard" is renamed to "Switching between
input methods" and allows to select "Switch to last used", which was the
default in older releases.

* Disable selection mode in text editors

Selection mode removes the space bar key (which is replaced by the Esc
key) and can be annoying in Emacs for example.
Text editor users probably have the `esc` key available.

* Refactor: Move EditorInfo related code to EditorConfig

Add the new EditorConfig class that handles configuration extracted from
the EditorInfo. It is accessible from the Config class for convenience.

This aims at reducing the length of already large classes and group the
code that was spread over several classes.

The number row option is changed into a ListPreference and controls whether the number row contains symbols or not.

Co-authored-by: Joey Schaff <j@jaoh.xyz>

This is mostly useful for characters that do not fit on a single 16-bit
char.
Shift sequences for 𝕨𝕩𝕗𝕘𝕤 are added for illustration.

Extra keys were ordered randomly everytime the settings were changed.
Now, there's a single ordering for each combinations of options in the
settings.

When the numpad is visible, remove the digits and arithmetic symbols
from the main layout. Similarly to when the number row is added.

This doesn't fix a bug but remove some tricky code. The shift key is no
longer different when the "double tap for capslock" option is on.
The handling of the option is moved to Pointer instead and becomes
simpler.