Move src/images to src/encode

This better aligns to include/encode and more accurately describes what
files in the folder do (encode pixels into .png, .jpeg, etc).

Change-Id: Ib85a6417ed4b03b9a02cc19582fddfc7d3802dbd
Bug: skia:13983
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/644318
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
27 files changed