Add captureDisplay API in WMS.

Allow clients to request a display screen capture using a specified
displayId. The caller can pass in their own required arguments and they
will get the screenshot via an async callback directly from SF.

Test: ScreenshotTests
Test: WindowManagerServiceTests#testCaptureDisplay
Bug: 242714168
Change-Id: If56bdf7aae07120e94cdb11bc6620302a886e585