Enhancements and minor bug fixes

[anoopmsivadas]

• Closes Do not learn from user input if input context has capaibilty flags with password/sensitive bit set #4.
• Closes Improvement to the IME typing UX #7.
• Handled word break characters properly.
• Added a basic workflow for meson build.

[anoopmsivadas]

Apparently Ubuntu 20.04 repository has an older Fcitx5 version, and it lacks APIs that we use. The Meson setup stage would succeed with 20.04 if we install libfcitx5core-dev, libfcitx5config-dev, libfcitx5utils-dev and a newer version of CMake from Kitware APT repo. But it would fail at compilation due to the Fcitx5 version.