Context sharing not implemented for many platforms

[mitchmindtree]

This is a tracking issue for the state of context display list sharing for each backend.

• Linux | Wayland | EGL
• Linux | X11 | EGL
• Linux | X11 | GLX
• Windows | WGL
• Windows | EGL
• macOS
• iOS
• Android

[sinesc]

I ran into unimplemented! on X11 GLX and wanted to see if I could potentially implement support. However, my test application already properly rendered to all three windows after simply removing the unimplemented macro (and creating the context with_shared_lists). Is it possible X11 GLX has either already been implemented or doesn't need any special support?

[goddessfreya]

Linux support + windows w/ egl has been added in #1101.