Apply effective base and max level on GL backend This works around GL drivers that neglect to clamp the base level or max level of immutable textures. BUG=angleproject:596 BUG=610800 TEST=angle_end2end_tests Change-Id: Ie4e04aaa9253f2befd73bccefa7759486b3ef487 Reviewed-on: https://chromium-review.googlesource.com/344590 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>