Drilldown class updates to match core

[mcoker]

placeholder for patternfly/patternfly#5274

It would probably be useful to introduce classes on the drilldown menu that give us finer control over targeting/styling elements based on their state as the menu is modified.

This comment provides an example of the intended update.

patternfly/patternfly#5271 (comment)

cc @thatblindgeye

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Jira Issue: PF-154

[nicolethoen]

#8469 commented out related Menu tests commented out. They need to be fixed/re-enabled.

Also, the drilldown examples/demos in Menu and Nav are broken and need to be fixed as part of this