CL: Add some event/memory helper functions Add the following helper functions on the CL frontend - check for user event - check for CL image/buffer types And on the VK backend - For CLBufferVk/CLImageVk much of the state is encoded in the front-end object. Add utility functions to get handle to them. - check for user event dependency in commandqueue Bug: angleproject:378103912 Change-Id: Ie76b44445ce2db3b5a49ccc6afe02e75c474875d Signed-off-by: Gowtham Tammana <g.tammana@samsung.com> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6004683 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>