Added nullable to most Content.Shared files (#3238)

* Add nullable to some Content.Shared files.

* Use [NotNullWhen(true)]

* Undo adding now redundant !'s

* Forgot one

* Add a ton more nullable

* You can guess

* Fix some issues

* It actually compiles now

* Auto stash before merge of "null2" and "origin/master"

* I lied

* enable annotations -> enable

* Revert ActionBlockerSystem.cs to original

* Fix ActionBlockerSystem.cs

* More nullable

* Undo some added exclamation marks

* Fix issues

* Update Content.Shared/Maps/ContentTileDefinition.cs

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

* Resolve some issues

* Remove unused method

* Fix more issues

* Fix more issues

* Fix more issues

* Fix more issues

* Fix issue, rollback SharedGhostComponent.cs

* Update submodule

* Fix issue, invert some if-statements to reduce nesting

* Revert RobustToolbox

* FIx things broken by merge

* Some fixes

- Replaced with string.Empty
- Remove some exclamation marks
- Revert file

* Some fixes

* Trivial #nullable enable

* Fix null ables

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>
Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Shared/GameObjects/Components/SharedCrayonComponent.cs

@@ -1,4 +1,5 @@
-using Robust.Shared.GameObjects;
+#nullable enable
+using Robust.Shared.GameObjects;
 using Robust.Shared.Maths;
 using Robust.Shared.Prototypes;
 using Robust.Shared.Serialization;
@@ -13,8 +14,8 @@ namespace Content.Shared.GameObjects.Components
         public override string Name => "Crayon";
         public override uint? NetID => ContentNetIDs.CRAYONS;
 
-        public string SelectedState { get; set; }
-        protected string _color;
+        public string SelectedState { get; set; } = string.Empty;
+        protected string _color = "white";
 
         [Serializable, NetSerializable]
         public enum CrayonUiKey
@@ -73,12 +74,12 @@ namespace Content.Shared.GameObjects.Components
     [Serializable, NetSerializable, Prototype("crayonDecal")]
     public class CrayonDecalPrototype : IPrototype
     {
-        public string ID { get; private set; }
+        public string ID { get; private set; } = string.Empty;
 
-        private string _spritePath;
+        private string _spritePath = string.Empty;
         public string SpritePath => _spritePath;
 
-        private List<string> _decals;
+        private List<string> _decals = new();
         public List<string> Decals => _decals;
 
         public void LoadFrom(YamlMappingNode mapping)
@@ -86,7 +87,7 @@ namespace Content.Shared.GameObjects.Components
             var serializer = YamlObjectSerializer.NewReader(mapping);
 
             serializer.DataField(this, x => x.ID, "id", string.Empty);
-            serializer.DataField(ref _spritePath, "spritePath", "");
+            serializer.DataField(ref _spritePath, "spritePath", string.Empty);
             serializer.DataField(ref _decals, "decals", new List<string>());
         }
     }