Wire up mouse and keyboard events in CanvasKit viewer

Change-Id: I10b57f18edb516b48be3ba16f98a540370ec689f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/292793
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
3 files changed