Implement keyboard-filter-experimental

[dcz-self]

Instructions for verifying are in https://codeberg.org/dcz/stiwri/src/branch/filter . Copying the requirements:

Use anvil from https://github.com/dcz-self/smithay/tree/filter

Start anvil:

git clone https://github.com/dcz-self/smithay
git checkout origin/filter
cd smithay/anvil
cargo run --winit

The demo application is anything supporting text-input.

WAYLAND_DISPLAY=wayland-1 yad --entry

This includes the "actions" MR: #511