util: Add calls for createImage* and destroyImage* to GLWindow This adds the interface to the GLWindowBase, an implementation to EGLWindow, and placeholder functions to WGLWindow. Bug: angleproject:4964 Change-Id: Ia13f5237500cece9564910c95c6c5eea67ca022d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3637559 Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Gert Wollny <gert.wollny@collabora.com>