Hide shrinkToFit -- not needed now that we have pathbuilder

Step one is to make it private -- only skottie needs it at the moment
Stpe two is to modify pathops to use builders, and then we can likely
remove it shrinkToFit entirely (since builder.snapshot() is already snug).

bug: skia:9000

Change-Id: I9126bcb6fc2094fbeede2acb1f211b0ab771feba
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/327341
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
7 files changed