Is your feature request related to a problem? Please describe.

I just tried out the new Mermaid inheritance diagrams - thanks for implementing them :)

I noticed that they only include the super classes that are part of the current documentation, unlike the show_bases option.

Describe the solution you'd like

The inheritance diagrams should include at least all bases mentioned by show_bases. External superclasses, which have further superclasses, could be included fully or truncated at the first external parent with a ... marker showing that something was truncated.