Rename SkTArray::reserve to reserve_back.

The semantics of `vector::reserve` and `SkTArray::reserve` were not the
same. SkTArray::reserve takes a delta over the current array size,
whereas vector takes a total array size. This could lead to subtle
errors with over- or under-reservation, hurting performance.

This CL renames `SkTArray::reserve` to `SkTArray::reserve_back` to give
the SkTArray behavior a distinct (hopefully easily understandable) name,
leaving its functionality as-is.

Change-Id: Icbd3114bb317fd5f307f393c02ae6fb6f83764e9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/326956
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
32 files changed