[openimageio] update to 2.1.16

[pwm1234]

Library name: openimageio

New version number: 2.1.16

Other information that may be useful (release notes, etc...)
There is a large list of improvements that have been made in openimageio since the 2.1.9 release in December 2019. I request that the openimageio port be updated to the current 2.1.16 release version.

Please let me know if there is something that I can do to help accelerate incorporation of this new version.

Thanks for your work on vcpkg--it does make my development work more productive!

[pwm1234]

Thank you!