Fix building against libglvnd-provided EGL headers
Add missing EGL/eglmesaext.h include. When building against mesa-provided headers, this header is included indirectly via EGL/eglext.h.
Also fix typo COGL_EGL_INCLUDE -> COGL_EGL_INCLUDES
Add missing EGL/eglmesaext.h include. When building against mesa-provided headers, this header is included indirectly via EGL/eglext.h.
Also fix typo COGL_EGL_INCLUDE -> COGL_EGL_INCLUDES