rename SkMipMap to SkMipmap

Change-Id: I1fa8a0482a717847236a30b4851061f4074b7755
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/302644
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Reed <reed@google.com>
48 files changed