Pyvista: bug with vtkMassProperties as pv.Cube().area return 0.0

[tkoyama010]

But the areas are not equal....

def get_area(mesh):
    return sum(mesh.compute_cell_sizes(length=False, area=True, volume=False,)["Area"])

import pyvista as pv

mesh = pv.Cube()
shrunk = mesh.shrink(0.8)

>>> get_area(mesh), get_area(shrunk)
(6.0, 3.840000114440919)

Also. there must be a bug with vtkMassProperties as shrunk.extract_surface().area return 0.0

_Originally posted by @banesullivan in https://github.com/pyvista/pyvista/pull/913#discussion_r499108567_

[banesullivan]

Perhaps we just change the area property to be:

@property
def area(self):
    return np.sum(self.compute_cell_sizes(length=False, area=True, volume=False,)["Area"])

[banesullivan]

Also. the suspect code:

>>> import pyvista as pv
>>> pv.Cube().area
0.0

whereas:

>>> np.sum(pv.Cube().compute_cell_sizes(length=False, area=True, volume=False,)["Area"])
6.0

[tkoyama010]

Fixed in #933