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/Research/SharedMaterialStorageComponent.cs

@@ -1,7 +1,7 @@
+#nullable enable
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using Content.Shared.Materials;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Serialization;
 using Robust.Shared.ViewVariables;
@@ -11,7 +11,7 @@ namespace Content.Shared.GameObjects.Components.Research
     public class SharedMaterialStorageComponent : Component, IEnumerable<KeyValuePair<string, int>>
     {
         [ViewVariables]
-        protected virtual Dictionary<string, int> Storage { get; set; }
+        protected virtual Dictionary<string, int> Storage { get; set; } = new();
         public override string Name => "MaterialStorage";
         public sealed override uint? NetID => ContentNetIDs.MATERIAL_STORAGE;
 
@@ -25,17 +25,6 @@ namespace Content.Shared.GameObjects.Components.Research
             }
         }
 
-        public int this[Material material]
-        {
-            get
-            {
-                var ID = material.ID;
-                if (!Storage.ContainsKey(ID))
-                    return 0;
-                return Storage[ID];
-            }
-        }
-
         /// <summary>
         ///     The total volume of material stored currently.
         /// </summary>