Convert planar 8 bit formats to planar 16 bit formats.

Includes msan fix for Convert8To16Row_Opt unittest.

I420 is YUV bt.601 8 bits per channel with 420 subsampling.
I010 is YUV bt.601 10 bits per channel with 420 subsampling.
I is color space - bt.601.  The function does no color space
 conversion so H420ToI010 is aliased to this function as well.
0 = 420 subsampling.  The chroma channels are half width / height.
10 = 10 bits per channel, stored in low 10 bits of 16 bit samples.

For SSSE3 version:
out/Release/libyuv_unittest --gtest_filter=*LibYUVConvertTest.I420ToI010_Opt --libyuv_width=1280 --libyuv_height=720 --libyuv_repeat=999 --libyuv_flags=-1 --libyuv_cpu_info=-1
[ RUN      ] LibYUVConvertTest.I420ToI010_Opt
[       OK ] LibYUVConvertTest.I420ToI010_Opt (276 ms)

Bug: libyuv:751
Test: LibYUVConvertTest.I420ToI010_Opt
Change-Id: I072876ee4fd74a2b74f459b628838bc808f9bdd2
Reviewed-on: https://chromium-review.googlesource.com/846421Reviewed-by: Miguel Casas <mcasas@chromium.org>
Commit-Queue: Frank Barchard <fbarchard@chromium.org>