Add Github Actions CI Workflow to build/test on Ubuntu 22.04

[13rac1]

Builds the library, demo, and runs the validator. This will help avoid a broken build in the future.

meson.build has been updated to capitalize the GLUT dependency name so it is detected correctly by Meson. Is this an issue on other architectures?

Note: Github CI runners are Ubuntu 22.04, which has an old version of harfbuzz, so harfbuzz must be built from source. The harfbuzz build can be removed when Github updates the CI runners to Ubuntu 24.04.

An example workflow build log is available here: https://github.com/13rac1/glyphy/actions/runs/5457958933/jobs/9932527922

[13rac1]

I had to figure this out to compile locally, so it wasn't much of a reach to set up the CI. You may not want CI on this project, feel free to close without merge. 😀

[behdad]

Thanks!