Add eglQueryDisplayAttribANGLE based on eglQueryDisplayAttribEXT to add
behavior for quering the count of all workarounds available. Used
externally to build a list of workarounds.

Bug: angleproject:1621

Change-Id: I793acedc76111fd018600169d58bf5d8cf4a63ee
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1637817
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>