Improve doc comments for SkTArray.

Change-Id: Ife5abd41cdc594abd20518081f8ed12565db4a47
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/291937
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Derek Sollenberger <djsollen@google.com>
2 files changed