Add EGL-based backend for wxGLCanvas

Among other things, this enables wxGLCanvas to be used natively on
Wayland.

Closes https://github.com/wxWidgets/wxWidgets/pull/2038

Closes #17702.

build/cmake/init.cmake

@@ -385,6 +385,9 @@ if(wxUSE_GUI)
             set(OPENGL_LIBRARIES "-framework OpenGLES" "-framework QuartzCore")
         else()
             find_package(OpenGL)
+            if(WXGTK3 AND OpenGL_EGL_FOUND)
+                set(wxUSE_GLCANVAS_EGL ON)
+            endif()
         endif()
         if(NOT OPENGL_FOUND)
             message(WARNING "opengl not found, wxGLCanvas won't be available")