Add Czech keyboard layouts

Two variants:

* Czech Standard (= qwertz)

* Czech qwerty

The accented letters layout corresponds to the UCW [1] layout shipped
with xkb, so we follow this precedent.

Like the DE layout, and unlike the US layout, the CZ layout has a
comma key and a narrower space bar. The added comma key also serves as
a visual balance to the added accents key, to keep the spacebar
centered.

The layouts have been tested manually on PinePhone.

[1] c60b77ea51/test/data/symbols/cz (L180)

tests/meson.build

@@ -51,6 +51,8 @@ foreach layout : [
     'us', 'us_wide',
     'br',
     'be', 'be_wide',
+    'cz', 'cz_wide',
+    'cz+qwerty', 'cz+qwerty_wide',
     'de', 'de_wide',
     'dk',
     'es',