Make onCreateScalerContext return unique_ptr.

Change SkTypeface::onCreateScalerContext to return std::unique_ptr
instead of a bare pointer. The public SkTypeface::createScalerContext
implementation already returns std::unique_ptr, so this is an internal
change only.

Move SkTypeface::createScalerContext implementation from
SkScalerContext.cpp to SkTypeface.cpp for consistency.

Also change the return type of SkScalerContext::MakeEmptyContext to
std::unique_ptr and rename to SkScalerContext::MakeEmpty.

Change-Id: I965308e8f9c78b887811e428f0de873dc6196479
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/346658
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Ben Wagner <bungeman@google.com>
21 files changed