Sound Specifiers. (#4239)

* Adds SoundSpecifier and a type serializer.

* DiceComponent makes use of SoundSpecifier.

* When rider autorefactoring decices to add field:

* Remove SoundEmptySpecifier, use nullable everywhere

Content.Shared/Sound/SoundSpecifier.cs

@@ -0,0 +1,67 @@
+using System;
+using Content.Shared.Audio;
+using Robust.Shared;
+using Robust.Shared.Serialization.Manager.Attributes;
+using Robust.Shared.Serialization.TypeSerializers.Implementations;
+using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom.Prototype;
+using Robust.Shared.Utility;
+
+namespace Content.Shared.Sound
+{
+    [DataDefinition]
+    public abstract class SoundSpecifier
+    {
+        public abstract string GetSound();
+    }
+
+    [DataDefinition]
+    public sealed class SoundPathSpecifier : SoundSpecifier
+    {
+        public const string Node = "path";
+
+        [DataField(Node, customTypeSerializer:typeof(ResourcePathSerializer), required:true)]
+        public ResourcePath? Path { get; }
+
+        public SoundPathSpecifier()
+        {
+        }
+
+        public SoundPathSpecifier(string path)
+        {
+            Path = new ResourcePath(path);
+        }
+
+        public SoundPathSpecifier(ResourcePath path)
+        {
+            Path = path;
+        }
+
+        public override string GetSound()
+        {
+            return Path == null ? string.Empty : Path.ToString();
+        }
+    }
+
+    [DataDefinition]
+    public sealed class SoundCollectionSpecifier : SoundSpecifier
+    {
+        public const string Node = "collection";
+
+        [DataField(Node, customTypeSerializer:typeof(PrototypeIdSerializer<SoundCollectionPrototype>), required:true)]
+        public string? Collection { get; }
+
+        public SoundCollectionSpecifier()
+        {
+        }
+
+        public SoundCollectionSpecifier(string collection)
+        {
+            Collection = collection;
+        }
+
+        public override string GetSound()
+        {
+            return Collection == null ? string.Empty : AudioHelpers.GetRandomFileFromSoundCollection(Collection);
+        }
+    }
+}