Tell `FindOSL.cmake` where to find the shader header files. These have
moved from `${LIBDIR}/osl/shaders` to `${LIBDIR}/osl/share/OSL/shaders`
when OSL was upgraded (T85365).
Fix package name missmatch in a few module files. IE "ALEMBIC" was
defined in the file but the find_package commands used "Alembic"
Some modules state that they set and use the _LIBRARY variable but the
do in fact not do this. Removed these comments from those files.
