SkEncoder: Rename files, change webp API, for consistency


Bug: skia:
Change-Id: I3dd6feb3d5661dcad3d2388b4d01fa9d3bbb15bb
Reviewed-on: https://skia-review.googlesource.com/15631
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
11 files changed