Expose more SkPicture and SkDrawable APIs

[mattleibow]

Description of Change

Add a few more APIs for SkPicture.

SkiaSharp Issue

Related to mono/SkiaSharp#2881

API Changes

size_t sk_drawable_approximate_bytes_used(sk_drawable_t* drawable);

void sk_picture_playback(const sk_picture_t* picture, sk_canvas_t* canvas);
int sk_picture_approximate_op_count(const sk_picture_t* picture, bool nested);
size_t sk_picture_approximate_bytes_used(const sk_picture_t* picture);

Behavioral Changes

None.

Required SkiaSharp PR

Requires mono/SkiaSharp#2883

PR Checklist

• Rebased on top of skiasharp at time of PR
• Changes adhere to coding standard
• Updated documentation