Migrate to ScreenshotData object

Instead of passing around a handful of objects, use a single object to
represent the accumulated state in the processing pipeline.

This is to facilitate the passing of screenshot metadata (in a later
CL).

Flag: All behavior changes are protected by SCREENSHOT_METADATA flag,
      several methods in the acquisition pipeline have been forked to
      use the new data structure.

Bug: 265075469
Test: atest RequestProcessorTest
Test: atest TakeScreenshotServiceTest
Test: atest ScreenshotDataTest
Change-Id: I65b996215a7c0cc2040390cca5876c22cb216b22