Remove duplicated class vtkTextureArray

Occurrences:

• Interaction/Widgets/vtkTexturedButtonRepresentation2D.cxx
• Interaction/Widgets/vtkTexturedButtonRepresentation.cxx

This was discovered while working on !8885 (merged).

It is important to avoid duplicated symbol names to avoid violating the ODR (One Definition Rule).

For some more context, see https://discourse.slicer.org/t/transition-of-nightly-build-from-vtk-9-0-20201111-to-9-1-20220125/21669/

Proposal approaches:

1. Move each vtkTextureArray to vtkTexturedButtonRepresentation::vtkTextureArray and vtkTexturedButtonRepresentation2D::vtkTextureArray

2. Rename vtkTextureArray respectively to vtkTexturedButtonRepresentationTextureArray and vtkTexturedButtonRepresentation2DTextureArray

3. Identify similar use of text array in the toolkit and create a dedicated vtkTextureArray class

I suggest to move forward with approach 1

cc: @ken-martin