Add the possibility to test both integrated and discrete GPU
with ANGLE tests. Previously it was using only discrete.

The binaries need the NSSupportsAutomaticGraphicsSwitching bundle
property.

This is needed to test ANGLE_power_preference.

Changes the behavior of test apps:

Previously,
  ./angle_end2end_tests
would use discrete GPU.

After,
  ./angle_end2end_tests
or
  ANGLE_PREFERRED_DEVICE=intel ./angle_end2end_tests
will use integrated GPU.
  ANGLE_PREFERRED_DEVICE=amd ./angle_end2end_tests
will use discrete GPU.

Bug: angleproject:7093
Change-Id: Ia64f6024e3215e69c2a1bde3ba4f67c3ca595476
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3516114


Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>