* gen_method_xml.py: Warn for unused dictionaries

Helps catch missing locales.

* Add languages for which a dictionary is available

Make dictionaries are available to more languages. Extra keys are added
for as many languages as possible but no layout is added.

Some languages are still not added, mainly because they use a script
that the keyboard doesn't support yet:

    pa, gu, or, te, mai, sat, km, iw, zgh, sd, ml, sa

The "en" locale, which was meant to be the default for English locales
that are not in the list, was used instead of exact locales like "en_US".

The "en" locale was also used as the default locale for languages that
are not in the list at all. The "en_GB" locale is used for this instead.

* Fix the spacebar in Hangul combining

The encoding for the spacebar changed and the Hangul combining code was
not updated.

* Change the default layout for Korean

Change default unknown locale dictionary from en_US to en_GB

This adds dictionary-based spell checking to the keyboard. The keyboard looks at the word being typed and matches it against a dictionary to either complete the rest of the word or find alternative spellings.

The core of this feature is implemented in cdict, which is included as a
submodule in vendor/cidct.

Cdict is developped at https://github.com/Julow/cdict
The dictionaries are hosted at https://github.com/Julow/Unexpected-Keyboard-dictionaries/
The wordlists used to build the dictionaries are the same ones used by
HeliBoard from https://codeberg.org/Helium314/aosp-dictionaries

- Add an activity accessible from the launcher app that lists available
  dictionaries with a download button.
  The DictionaryListView view shows the list of available dictionaries and
  handles downloading and installing them.

- The Dictionaries class manages installed dictionaries. Dictionaries are
  installed as individual files into the app's private directory.

- Available dictionaries are listed in dictionaries.xml, which is generated
  when building Unexpected-Keyboard-dictionaries.
  method.xml mentions the dictionary name for each locales.

Locale are now defined in `gen_method_xml.py` in a more convenient and
checked way. It contains both the locale definition and the generation
script.

`method.xml` is generated with:

    gradle test

The goal is to support dictionaries for spell checking.

This adds the English, Hausa, Yoruba and Igbo languages for Nigeria. The
goal is to add the ₦ symbol as well as basic support for these
languages. No layout is added.