Remove encodeToData from CanvasKit and documentation

Follow-up to https://skia-review.googlesource.com/c/skia/+/667296

This adds gn arguments so clients can explicitly disable certain
encoders without having to use #ifdefs.

Change-Id: I49b9e2db3b268eaf4171b720ebfed09472af3859
Bug: skia:13983
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/669916
Reviewed-by: Leon Scroggins <scroggo@google.com>
6 files changed