Add functional `glxgears` `glxgears-32`

[Ikey Doherty]

Got the package ready, we'll need LSI to expose the bulk of the shim as a new lsi-exec binary that we can utilise within the snap. This will let us execute other commands such as glxgears while letting LSI perform all the necessary bootstrap of the environment, and then ensure any process launched is done so in an identical fashion to how we launch Steam.

This will let us expose 4 new apps:

• glxgears
• glxgears-32
• glxinfo
• glxinfo-32

This is purely for debugging LSI compatibility, and allowing users to verify their drivers work correctly when getting Steam installed. From our perspective we can ask anyone who opens a bug report about steamui.so libGL.so.1 style errors to first run snap run linux-steam-integration.glxgears-32 to actually verify they have 32-bit driver support.