Revise swapchain management in sk_app.

This is mainly to move the Recorder snap for Graphite to a common
location (WindowContext).

Change-Id: I6a905b28ead43af5536421de6791ea70a00ac889
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/669177
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
37 files changed