[Analyzer] Add a way to add inherit properties to element in manifest instead of superclass

[maicol07]

Should this be an RFC?

• This is not a substantial change

Which package is this a feature request for?

Analyzer (@lit-labs/analyzer)

Description

Components that inherit other Lit webcomponents don't inherit properties (but just set the superclass field). This breaks the compatibility with external tools.
See: break-stuff/cem-tools#69

Alternatives and Workarounds

CEM analyzer works fine

[justinfagnani]

We could possibly add an option for this (contributions accepted!) but tools really should read superclass and mixin properties.