BUG #13706: enable VTK_CURSOR_CROSSHAIR for vtkXOpenGLRenderWindow

With cursor themes, XC_crosshair is a perfectly nice cursor under X,
so it makes no sense to fall back to an arrow cursor instead.

Work for this fix has been sponsored by BP.

Change-Id: I08a3d4e3e34cd26db36abb701efa74f306eb1a5f
Merge topic 'release-vtkXOpenGLRenderWindow-fixes' into master

85499309 BUG #13706: enable VTK_CURSOR_CROSSHAIR for vtkXOpenGLRenderWindow