fix(OpenGLImageMapper): use typed array for scalars
fix(OpenGLImageMapper): use typed array for scalars

Co-Authored-by: Forrest Li <11d4423a8d0e2275b9f4d5550c79113564211217@kitware.com>

Kitware/vtk-js,Kitware/vtk-js,Kitware/vtk-js,Kitware/vtk-js