keyboard: Only generate keycodes from an allowlist

Some broken clients (most notably Chromium and its descendants)
try to interpret keymaps as if they were input sequences coming
from evdev. Workaround that by only using codes that directly
produce characters.

Fixes #244

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/598>

src/lib.rs

@@ -31,6 +31,7 @@ mod event_loop;
 pub mod float_ord;
 pub mod imservice;
 mod keyboard;
+pub mod keycodes;
 mod layout;
 mod locale;
 mod main;