Missing errors for enum shapes without members

[milesziemer]

Take the following model:

$version: "2"

namespace smithy.example

enum Foo {}

Building this model fails with something like:

ERROR: smithy.example#Foo (Model)
     = enum must have at least one entry

But the language server does not give any highlighting or underlying indicating that enums must have at least one entry.

[daddykotex]

I found that the issue originates from smithy-model. This is because we're missing the location for the SyntheticEnumTrait that's created and where the validation happen. Because the location is not there, the language server can bind the validation error to a Diagnostic on a file.

Tested with a local publish: