Improved validation logic for Missing Asset Wrapper Plugin

[kharrop]

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

Currently, we are relying on the message string because we don't have access to the type information that is associated with AssetWrapperOrSwitch.

Describe the solution you'd like

Potentially we could attach more information to the Diagnostic so we could leverage that instead of the message, or add an API to PlayerContent to return an XLR node that represents the expected type at a given JSON node position since we could then use xlrNode.name.