Reland "Respect full precision for RGB16 PNGs" (part 1)

Reland "Respect full precision for RGB16 PNGs" (part 1)

This is just the new test images.

I'm relanding this in pieces to try to bisect a
strange MSAN error.

Original CL:
https://skia-review.googlesource.com/c/7085/

BUG=skia:

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD,Build-Ubuntu-Clang-x86_64-Release-Fast,Test-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Debug-MSAN

Change-Id: Iec6b8cf52134992591651bf46bd6cd67d53fad52
Reviewed-on: https://skia-review.googlesource.com/7201
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>