rename atlassize->atlasdimensions

Change-Id: I0262ed26f0b3523302bbb4e94dfca94d120fc70c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249980
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
10 files changed