Give silicons proper lobby/character editor previews (#33763)

* Give silicons proper lobby/character editor previews

No more naked dummies, properly show a borg/AI sprite now.

This means taking the JobEntity into account when spawning the dummy. For AIs I had to add a "JobPreviewEntity" field because they'd look like a posibrain otherwise. AI therefore uses a custom dummy entity I defined.

Also I had to add some margins to the UI, because otherwise the 32x32 sprite of the AI would look bad.

* Update Content.Shared/Roles/JobPrototype.cs

* Update Content.Client/Lobby/LobbyUIController.cs

* Update Resources/Prototypes/Entities/Mobs/Player/silicon.yml

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Co-authored-by: slarticodefast <161409025+slarticodefast@users.noreply.github.com>

Content.Shared/Roles/JobPrototype.cs

@@ -119,6 +119,13 @@ namespace Content.Shared.Roles
         [DataField("jobEntity", customTypeSerializer: typeof(PrototypeIdSerializer<EntityPrototype>))]
         public string? JobEntity = null;
 
+        /// <summary>
+        /// Entity to use as a preview in the lobby/character editor.
+        /// Same restrictions as <see cref="JobEntity"/> apply.
+        /// </summary>
+        [DataField]
+        public EntProtoId? JobPreviewEntity = null;
+
         [DataField]
         public ProtoId<JobIconPrototype> Icon { get; private set; } = "JobIconUnknown";