* Better spell check with cursor in the middle of a word

Suggestions are based on the entire word and no longer the part of the
word just before the cursor. Also, tapping a suggestion or the space bar
autocorrect replaces the entire word.

* Reduce the number of calls to refresh_current_word

While the cursor moves, calls to refresh_current_word are now only done
when the cursor exits the current word.

* 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.

* Refactor: Create subpackage 'suggestions'

* Candidates view: Status message when no dictionary installed

Show a message on the candidates view instead of leaving it empty. A
button points to the dictionary installation activity.

* Add an option to disable the suggestions

* Refactor: Remove Config.should_show_candidates_view

This was moved to EditorConfig.

* Don't disable text suggestions in some text boxes

* Suggestion text size matching settings

The candidates view height is based on the height of keyboard rows and
the suggestion text size is based on the size of labels on the keys.

This is influenced by symbol size and keyboard height options.

* Refactor: Split DeviceLocales out of Keyboard2

This moves the code from Keyboard2 that handles the active IME subtypes
and the current one.

The goal is to access this information from the dictionary activity
while simplifying the code of Keyboard2.

* Refresh the candidates view when subtype changes

This fixes the status message being inconsistently shown.

* Refactor: Load DeviceLocales less often

Previously, [DeviceLocales.load()] was called everytime the keyboard was
shown on the screen. This operation is moderately costly and only need
to be done when the IME subtype changes.

* EditorConfig: Fix crash on Android 9

The `CurrentlyTypedWord` class tracks the word that is being typed. It's
implemented on the same model as Autocapitalisation and avoid expensive
IPC calls when possible.

The `Suggestions` class is where the suggestion lookup should go. It
currently just echoes the current word.

* 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.