Mesh.face_attributes does not return all attributes

[Achillx]

Describe the bug
Mesh.face_attributes(fkey) only returns the default attributes that have been set using Mesh.update_default_face_attributes().

To Reproduce
Run the code bellow:

from compas.geometry import Box
from compas.datastructures import Mesh

box = Box.from_width_height_depth(2, 2, 2)
box = Mesh.from_shape(box)
box.update_default_face_attributes({"attr1":"value1", "attr2":"value2"})

random_fkey = box.get_any_face()
print(random_fkey, box.face_attributes(random_fkey))

box.face_attribute(random_fkey, "attr3", "value3")
print(random_fkey, box.face_attributes(random_fkey))
print(random_fkey, box.face_attribute(random_fkey, "attr3"))

Expected behavior
Return all attributes, including the ones that have been assigned only to that face

Desktop (please complete the following information):

• Compas: 0.18.1
• Python version: 3.7.6
• Python package manager: conda