Ability to mark an asset as editor only to stop it from being uploaded in non library projects

[QuackCola]

Summary

This PR enables users to mark an asset as EditorOnly to prevent it from being uploaded on a project that isnt a "library"

Motivation & Context

So that you can have "editor only" resources like shadergraph not get uploaded when uploading anything but a library.

Implementation Details

Added EditorOnly to AssetTypeFlags along with some basic checks in the Engine project and base editor library so that Resources marked like below dont get published when not uploading a library. The marked asset will also not be exported as part of a game export.

[AssetType( Name = "MyAsset", Extension = "mything", Category = "Custom", Flags = AssetTypeFlags.EditorOnly )]
public sealed class MyAsset : GameResource
{
}

Checklist

• Code follows existing style and conventions
• No unnecessary formatting or unrelated changes
• Public APIs are documented (if applicable)
• Unit tests added where applicable and all passing
• I’m okay with this PR being rejected or requested to change 🙂