Move SkFloatBits.h into src/base instead of include/private.

These are no longer used anywhere from inside `include/`. This
limits their exposure to client code.

I added a release note in case someone was accidentally relying
on these methods, since they existed in some example code despite
being private.

Change-Id: I26c92b83979b62484b7fd3e7d1f06e4b41c7ddb1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/842479
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: James Godfrey-Kittle <jamesgk@google.com>
Commit-Queue: James Godfrey-Kittle <jamesgk@google.com>
55 files changed