SkTArray to move when moving.

This updates SkTArray to move elements when possible, instead of always
copying them.

TBR=reed
Agreed moving is good. This should also become private.

Committed: https://skia.googlesource.com/skia/+/3c69348e725131150e4ab962dec1b3ff1148a6bd

Review URL: https://codereview.chromium.org/1672063002
4 files changed