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/Cargo/SharedGalacticMarketComponent.cs

@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Collections;
 using System.Collections.Generic;
 using Content.Shared.Prototypes.Cargo;
@@ -35,10 +36,10 @@ namespace Content.Shared.GameObjects.Components.Cargo
         ///     Returns a product from the string id;
         /// </summary>
         /// <returns>Product</returns>
-        public CargoProductPrototype GetProduct(string productId)
+        public CargoProductPrototype? GetProduct(string productId)
         {
             var prototypeManager = IoCManager.Resolve<IPrototypeManager>();
-            if (!prototypeManager.TryIndex(productId, out CargoProductPrototype product) || !_products.Contains(product))
+            if (!prototypeManager.TryIndex(productId, out CargoProductPrototype? product) || !_products.Contains(product))
             {
                 return null;
             }
@@ -75,7 +76,7 @@ namespace Content.Shared.GameObjects.Components.Cargo
                     _products.Clear();
                     foreach (var id in products)
                     {
-                        if (!prototypeManager.TryIndex(id, out CargoProductPrototype product))
+                        if (!prototypeManager.TryIndex(id, out CargoProductPrototype? product))
                         {
                             continue;
                         }