OSL v1.12.12.0

Release 1.12.12.0 -- 1 May 2023 (compared to 1.12.11.0)

• New ShadingSystem getattribute query for shader groups: "attribute_types"
  retrieves a pointer to the array of TypeDesc values describing the
  attributes retrieved by existing "attributes_needed" and "attribute_scopes".
  #1650
• Fix a bug with binding userdata when it's used by more than one shader
  within the group and they disagree about whether derivatives are needed when
  retrieving the attribute. #1673