SF: Move screenshot Surface ops off main thread

This change rearranges the various operations that correspond to
capturing a screenshot such that all of the Surface-related ones
(connect, dequeue, queue, disconnect) are performed on the incoming
Binder thread rather than on SurfaceFlinger's main thread. This has two
major benefits:

  1) It reduces the amount of time that the SurfaceFlinger main thread
     is blocked while performing a screenshot, often by a considerable
     amount. This should reduce the risk of jank when screenshots are
     taken, such as for task snapshots during window transitions.
  2) It means that the SurfaceFlinger main thread is not susceptible to
     being blocked by a badly-performing BufferQueue consumer. This
     also enables us to remove the GraphicProducerWrapper class, which
     was previously performing a similar role.

Finally, this change also adds a mechanism that detects if the
screenshot would have been performed between the two phases of normal
SurfaceFlinger operation (invalidate and refresh), and defers it if
this condition is detected. This should further reduce the risk of jank
as a screenshot will only occur between frames rather than in the
middle of a frame.

Bug: 62257775
Test: SurfaceFlinger_test and manual verification that screenshots
      still work
Change-Id: I23e6f088b4d6e477472dfc2a6c36ef3dd930c047