C#: Load assemblies as collectible only in the Godot editor

We use collectible AssemblyLoadContexts as that's the only way to allow
reloading assemblies after building. However, collectible assemblies
have some restrictions:

- https://learn.microsoft.com/en-us/dotnet/framework/reflection-and-codedom/collectible-assemblies#restrictions-on-collectible-assemblies

Those restrictions can cause issues with third-party code, such as some
mocking libraries.

In order to work around this problem, we're going to load assemblies
as collectible only in Godot editor, and not when running games.
These issues will still exist in the editor, but this will be enough
for some users.

modules/mono/csharp_script.cpp

@@ -710,6 +710,12 @@ void CSharpLanguage::reload_assemblies(bool p_soft_reload) {
 		return;
 	}
 
+	if (!Engine::get_singleton()->is_editor_hint()) {
+		// We disable collectible assemblies in the game player, because the limitations cause
+		// issues with mocking libraries. As such, we can only reload assemblies in the editor.
+		return;
+	}
+
 	// TODO:
 	//  Currently, this reloads all scripts, including those whose class is not part of the
 	//  assembly load context being unloaded. As such, we unnecessarily reload GodotTools.