This allows us to more easily compare sets of parameters used in our
tests. The config parameters are stuff like the red / gree / blue bits
used in an EGL config. Or particular sets of extensions or other
EGL options.

This will more easily allow us to determine when we need to use a new
EGL display instead of reusing a prior.

Bug: angleproject:3261
Change-Id: Ia1f0ede988e0b4084fbb4d55097e94fd89ee4899
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1531535
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>