Reject GL_HALF_FLOAT_OES on WebGL 2.0 This type enum is not exposed in WebGL 2.0 contexts. Skipped OES enum testing on ES 3.0 contexts in half-float texture WebGL compatibility tests. Bug: angleproject:7668 Change-Id: I56138aa686192a873b308ba58633e6a1fc808a1d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3900019 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>