libyuv: Update to r1871 (2a6cb743)

Changes from upstream:
https://chromium.googlesource.com/libyuv/libyuv/+log/d53f1bee..2a6cb743

The intention of the CL is to import the functions necessary to
enable AV1 (and AVIF) 12-bit color conversion.

Bug: 268505204
Test: Builds. Media and Camera CTS tests pass.
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:27750a13c6eaacb9f716da3fe1734a8d106d7ff4)
Merged-In: I756d3bd5047d4719659f9e1a449217b1940e51a4
Change-Id: I756d3bd5047d4719659f9e1a449217b1940e51a4
84 files changed