Only add necessary attributes in DataFilterExtension

[felixpalmer]

Closes #8694

Change List

• Allow 0 as value for filterSize & categorySize
• Only add attribute to shader for non-zero sizes
• Default categorySize to 0 to fix breaking change in v9
• Test & doc update

[coveralls]

coverage: 89.996% (+0.008%) from 89.988%
when pulling 9a34aec on felix/data-filter-opts
into f50bec4 on master.

[ibgreen]

Just thoughts around the theme that less conditional code could be a goal worth considering.

[ibgreen]

Looking at this, I ask myself if we really want to require an attribute that can be applied in both instanced and non-instanced usage should be renamed. This simple renaming adds a lot of clutter to this shader.

[Pessimistress]

Can you add a few render tests (data filter, category filter & both)?