Maintain input_method_secure patches

The code from https://source.puri.sm/Librem5/wlroots/commits/input_method_secure will not get merged to rootston upstream, and the maintainers refused it already. It's crucial to have input method support on any real device though. Until a better method comes, these patches need to be applied on top of master.

Since I don't know how to do that properly, I'm filing an issue.