Convert bookmaker to SkJSON

Verified that running bookmaker produces an identical fiddle.json
before and after this change.

Bug: skia:
Change-Id: I1aa7477348a5f8c362201199b130508c2818116f
Reviewed-on: https://skia-review.googlesource.com/c/188303
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
7 files changed