math/Imath: Update to 3.1.7, major lib ver. -> 30

Note this incurs a revision bump of ports using this because
the library major version has changed.

Announcement: https://github.com/AcademySoftwareFoundation/Imath/releases/tag/v3.1.7
Changelog: https://github.com/AcademySoftwareFoundation/Imath/blob/v3.1.7/CHANGES.md#version-317-March-1-2023

(Not intending to MFH.)