Store and check adapter features before using them

[hekno25]

This commit solves #33 by adding a wgpu::Features field to the Renderer struct and checking it before drawing the mesh or debug lines. The renderer does not inform the user if it is unable to use the POLYGON_MODE_LINE feature but it should at least prevent crashing. If this is too rudimentary I'd be glad to keep working on it and make the gui prevent mesh or debug rendering when the feature is missing.

[hannobraun]

Thank you, @hekno25, this looks great! Glad you found such a simple solution!

The renderer does not inform the user if it is unable to use the POLYGON_MODE_LINE feature but it should at least prevent crashing. If this is too rudimentary I'd be glad to keep working on it and make the gui prevent mesh or debug rendering when the feature is missing.

Informing the user is definitely desirable, and if you want to work on that, that would be very welcome. But this is already an improvement in itself, and I'm glad to merge it.

In general, I prefer merging a series of small improvement, over a big pull request that does everything perfect. Small changes are easier to review, cause less merge conflicts (thus less work for the contributor), and they reduce the risk of wasted work.