chore(doc-gen): add directive names that aren't params to usage section

When a directive can be used as an attribute or CSS class, but doesn't take 
a value, its name is not included in the parameters, which previously meant 
that the directive name was missing from the Attribute / CSS Class usage 
section of the docs.

This commit adds the name to the Usage section when it is missing
from the parameters.

Closes #14045
Closes #16265