ui/egl: Don't change bound GL context when creating new context

Don't change bound GL context when creating new GL context for consistency
with behavior expected by virglrenderer that assumes context-creation doesn't
switch context. eglCreateContext() doesn't require GL context to be bound
when it's invoked. Update qemu_egl_create_context() to spawn GL sub-contexts
from a given shared GL context instead of a currently-bound context.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Message-ID: <20260303151422.977399-4-dmitry.osipenko@collabora.com>
Message-ID: <20260304165043.1437519-6-alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>