GDK: GL context creation fails on Wayland with OpenGL < 3.0

The context creation path on Wayland fails when driver does not provide a OpenGL 3 context, even though it works with OpenGL 2.1 on X11 (and on Wayland after manually changing version values from 3 to 2 in gdk/wayland/gdkglcontext-wayland.c).

Gdk-Message: 06:56:03.379: Creating EGL context version 3.2 (debug:no, forward:no, legacy:no, es:no)
Gdk-Message: 06:56:03.379: eglCreateContext failed, switching to legacy
Gdk-Message: 06:56:03.379: Creating EGL context version 3.2 (debug:no, forward:no, legacy:no, es:no)
Gdk-Message: 06:56:03.379: eglCreateContext failed, switching to legacy
Gsk-Message: 06:56:03.379: Failed to realize renderer of type 'GskGLRenderer' for surface 'GdkWaylandToplevel': Unable to create a GL context

Gdk-Message: 06:56:03.379: Creating EGL context version 3.2 (debug:no, forward:no, legacy:no, es:no)
Gdk-Message: 06:56:03.379: eglCreateContext failed, switching to legacy
Gsk-Message: 06:56:03.379: Failed to realize renderer of type 'GskGLRenderer' for surface 'GdkWaylandToplevel': Unable to create a GL context

Gsk-Message: 06:56:03.379: Using renderer of type 'GskCairoRenderer' for surface 'GdkWaylandToplevel'

This can be tested by using MESA_GL_VERSION_OVERRIDE=2.1 environment variable.

Tried on master branch, commit 3d988d5f.