Fix racy global in gl::Compiler. We introduce a new Display Global Mutex in egl::Display that can guard access to gActiveCompilers in Compiler.cpp. Was detected by running MultithreadingTest against TSAN. Bug: b/168744561 Change-Id: I97866b60a173f60899cd0406fe0f71000035c0cf Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2415181 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>