Added new arguments for screenshot request

Added frameScaleX and frameScaleY to replace frameScale to allow callers
to specify an X and Y scale separately.

Added grayscale flag to allow the caller to take the screenshot
in grayscale.

Test: ScreenCaptureTest.CaptureWithGrayscale
Bug: 155825630
Change-Id: Iea043b7074707df897d80bf057d7cc3870afad89