Proper copy and move for path classes

SkPathBuilder and SkPath should be movable (avoids extra work in both
cases) and the default implementations should not be inline as they are
not trivial.

Change-Id: I31ee6b2b775c83e0b681e1dc6c2c1cf1357c8724
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1138116
Reviewed-by: Florin Malita <fmalita@google.com>
Auto-Submit: Ben Wagner <bungeman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>