OSL v1.12.8.0

Release 1.12.8.0 -- 3 Jan 2023 (compared to 1.12.7.1)

• Remove dependency on OptiX SDK for building core OSL with OptiX support.
  You can now build OSL with OptiX support enabled even if you don't have the
  OptiX SDK headers present at build time. But you will still need them to
  build your OptiX-based application that uses OSL for GPU rendering. #1627
• Batch mode: fix issue with closure keyword parameters. #1620
• Batch mode: fix crash when adding a default initialized closure. #1624
• Batch mode: Fix support for closures with array types. #1630
• testshade: better testing of all closure parameter types. #1621
• Fix various CI breaks as dependencies shifted. #1629 #1631 #1633