libwebp: updated to 1.2.2

version 1.2.2
  This is a binary compatible release.
  * webpmux: add "-set bgcolor A,R,G,B"
  * add ARM64 NEON support for MSVC builds
  * fix duplicate include error in Xcode when using multiple XCFrameworks in a
    project
  * doc updates and bug fixes

(adam)