Add `SharedOnlyEventAttribute` and analyzer

[Tayrtahn]

Adds an attribute that can be applied to event structs/classes to indicate that they should only be subscribed to in Shared code. Subscriptions to the event in Server-only code will raise a warning.

Applying the attribute to GetVerbsEvent:

Warning on a server-only subscription:

The attribute also has an optional parameter, AllowClientOnly which defaults to true. If true, subscriptions are also allowed in Client-only code. In most potential use cases (verbs, examines), Client-only subscriptions are fine.

This feature was requested by @slarticodefast to help enforce https://github.com/space-wizards/space-station-14/issues/39286 - subscribing to GetVerbsEvent in server-only code causes the verbs menu to jump around, because it is first populated client-side with Client and Shared verbs, then gets rebuilt when the server sends its version containing new entries. This is a major annoyance for players, and has caused problems where admins accidentally trigger actions on players while trying to use examining verbs on them.

[VerinSenpai]

Good freakin shit man!

[TornadoTechnology]

This engine clearly needs more cool analyzers. Awesome.

[Tayrtahn]

Would it not make more sense to have an attribute that worked with bitflags? Like [NetworkSideOnly(Shared | Client)]?

Yeah, I was thinking that too. Figured I'd do it this way first and upgrade to that if desired. I'll get on it.