Imgui integration renders incorrectly in some instances

[einarf]

After poking around the following was seen:

• self.wnd.size changes with the window size
• self.ctx.screen.size stays fixed at (1280, 720)

I'm wondering if we should do a detect_framebuffer on resize to ensure we have the right framebuffer information. Also consider querying the source information for screen and buffer sizes in BaseWindow so we don't rely on possibly stale information. There might also be events for framebuffer scaling changes.

Another theory is that the framebuffer retains the previous scissor box. We might also only want to rely on the framebuffer information from the window library.

[einarf]

fixed