jpegr codec: Implement scanline decoding and sampling

Add functionality needed for scanline decoding, region decoding and
sampling.

Test: atest BitmapFactoryTest#testDecodeJpegr BitmapRegionDecoderTest#testJpegr
Change-Id: I1557d9ee4a45802700b241f05fddaf50168512cb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/631162
Commit-Queue: Fyodor Kyslov <kyslov@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
4 files changed