fix(OpenGL): fix resampling of very large textures

When resizing, the memory alloc for textures with more than
4 Gig samples was overflowing int. Switch to size_t
Status Job ID Name Coverage
  External
passed cdash-buildbot

failed vtk@master-adora-linux-shared-release+cuda+gcc+mpi+optix+python2+tbb+vtkm

00:06:36

failed vtk@master-duma-linux-shared-release+osmesa+ospray

00:30:51

pending vtk@master-luigi-linux-shared-release+mpi+python2+tbb
failed vtk@master-taanab-linux-shared-release+adios2+mpi+python2

00:22:07