With this commit, we now survive a reinstall or upgrade of the nvidia
drivers on my Windows sytem without crashing.
This commit allows notifying the application of the context loss
so the application can either try to reinit opengl or open a new
window as a replacement and init opengl there.
I've not had success at reinitializing opengl after a driver upgrade;
it seems to be persistently stuck in a state where it fails to allocate
a vertex buffer.
SO, the state we have now is that we try to reinit opengl on a new
window, and if that fails, leave it set to the software renderer.
This isn't a perfect UX, but it is better than terminating!
refs: https://github.com/wez/wezterm/issues/156
