Unified display screenshot into one displayCapture function

Cleaned up SurfaceComposerClient display screenshot functions so there
is only function that takes a screenshot based on display token. It
accepts a DisplayCaptureArgs and returns ScreenCaptureResults object.

Test: Display screenshots + secure works
Test: adb shell screencap
Bug: 162367424

Change-Id: I5900f387c7533ae37d4159152bfaf106fb0391d4