Use EnumAdapters to properly detect primary GPU on Win EnumDisplayDevicesA returns the card that's connected to the display, but EnumAdapters return the adapter which the desktop primary is displayed at index 0. We can use this to determine the device used for graphics. Also cleans up the discrepancy between platforms on finding "primary" vs "active" GPU. Asserts that the GPU expected to run ANGLE commands is the active GPU, and deprecates the primary GPU to be equal to the active GPU. Bug: angleproject:3383 Change-Id: I422fba1bbe47d85b7c09e378d559eaebf89e2625 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1584360 Commit-Queue: Jonah Ryan-Davis <jonahr@google.com> Reviewed-by: Geoff Lang <geofflang@chromium.org>