Add entry point eglSignalSync
Update autogen files

Test: angle_deqp_egl_tests
--deqp-case=dEQP-EGL.functional.reusable_sync.*

Bug: angleproject:5168
Change-Id: I47afa4010c533096b4c56e9b3ab6eddc1944b83e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2472998
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jeff Vigil <j.vigil@samsung.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>