MDC List: Don't use aria-selected="true" on invalid roles

[abhiomkar]

As per ARIA spec aria-selected property is used only to specific roles.

[kfranqueiro]

Given that we previously augmented the List component to auto-detect activated behavior vs. selected, we may also be able to auto-detect the presence of roles in which aria-selected is valid, and in other cases opt for aria-current instead (which is the most semantically-correct attribute to use for drawer navigation).

I'm not sure if we'd want to simply build this in to the same check for activated vs. selected... it might work for now, but could still yield invalid combinations down the line.

[kfranqueiro]

This was resolved by #4055 insofar as ensuring the correct ARIA roles and attributes are applied within the context of List. We'll open a separate issue around aria-selected vs. aria-current.