Given a def id this checks if the parent def id (modulo modules) correspond to
the def id of the parent impl definition (the direct one and the outermost one).
Given a path, this checks if the if the parent resolution def id corresponds to
the def id of the parent impl definition (the direct one and the outermost one).
Return a “error message-able” ident for the last segment of the Path
Return for a given Path
the span until the last args
Given a DefId
checks if it satisfies f
if it does check with it’s parent and continue
until it doesn’t satisfies f
and return the last DefId
checked.