graphics/*openimageio: chase Imath, update->2.2.16

openimageio upstream versions received lots of build fixes for
Imath compatibility, so update to 2.2.16 from 2.2.13.
(oiio 2.2.13 does not build with Imath 3.1.0)

The patch fiddling is due to Ptex-related changes in openimageio's cmake
build system, https://github.com/OpenImageIO/oiio/pull/3001

Changelogs (one document to read through):
https://github.com/OpenImageIO/oiio/blob/v2.2.16.0/CHANGES.md#release-2216-1-jul-2021----compared-to-2215

or with clickable links to issues/merges:
https://github.com/OpenImageIO/oiio/releases/tag/v2.2.16.0
https://github.com/OpenImageIO/oiio/releases/tag/v2.2.15.1
https://github.com/OpenImageIO/oiio/releases/tag/v2.2.15.0
https://github.com/OpenImageIO/oiio/releases/tag/v2.2.14.0