Move worker pools to Display It doesn't make sense for each context to have its own set of CPU-count workers. This change also facilitates access to the thread pools where gl::Context is not available (but egl::Display is). Bug: b/250688943 Change-Id: I240353abba26c15338d59631b4179a58dfd662f5 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3961334 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>