Add binding.api.(Keyed)Instance{Identifier,Wildcard}

Our current use of yang.binding.InstanceIdentifier in mdsal-binding-api is rather unfortunate - with accidental feature (i.e. wildcards) and layering violation.

Add two basic concepts:

• InstanceIdentifier, covering the yang.binding.InstanceIdentifier wildcarded=false case
• InstanceWildcard, covering the yang.binding.InstanceIdentifier wildcarded=true case

These should work similarly to InstanceIdentifierBuilder as of MDSAL-798.

Compatibility to/from yang.binding.InstanceIdentifier should be covered with methods for each of the concepts:

class InstanceIdentifier {
    // Throws IAE if legacy is wildcarded
    static InstanceIdentifier ofLegacy(yang.binding.InstanceIdentifier legacy);

    // Always non-wildcarded
    yang.binding.InstanceIdentifier toLegacy();
}

class InstanceWildcard {
    // Throws IAE if legacy is *not* wildcarded
    static InstanceWildcard ofLegacy(yang.binding.InstanceIdentifier legacy);

    // Always wildcarded
    yang.binding.InstanceIdentifier toLegacy();
}