scanner: Add a --max-version argument

SDL recently hit a subtle compatibility breakage when users started building with version 1.20, resulting in the following patch:

https://github.com/libsdl-org/SDL/pull/5436

The short version: A system with 1.18 (for example) can build something that works on systems with 1.20, but building with 1.20 would silently succeed and then crash when loaded on systems with something older, even though the application code is entirely unchanged.

This has been fixed by enforcing 1.20-on-1.20, but to maximize compatibility we would like to have something that allows us to cap the expected client version, meaning systems with updated Wayland files can compile the same code without bumping the version requirements accidentally. For example, --max-version=1.18 would bring back the behavior from before this commit: 0e0274af