Improve type reporting in `UnknownArrayHandle`
Added features with reporting types with UnknownArrayHandle. First, added
a method named GetArrayTypeName that returns a string containing the type
of the contained array. There were already methods GetValueType and
GetStorageType, but this provides a convenience to get the whole name in
one go.
Also improved the reporting when an AsArrayHandle call failed. Before,
the thrown method just reported that the UnknownArrayHandle could not be
converted to the given type. Now, it also reports the type actually held by
the UnknownArrayHandle so the user can better understand why the
conversion failed.
Also fixed an issue where the GetValueType and GetStorageType were not
actually returning the correct type.