winex11: Drop pixmap-based child window workaround.
Updating the GL drawables on/offscreen dynamically, similarly to how we do it for Vulkan, and in order to ultimately converge and factor both GL and VK client surfaces.
Updating the GL drawables on/offscreen dynamically, similarly to how we do it for Vulkan, and in order to ultimately converge and factor both GL and VK client surfaces.