Clean a bunch of C# warnings

- `[Obsolete]` tag generated in the middle of documentation comments
- Potential `null` values in generators
- Obsolete call to `GetEditorInterface()`
- We don't want `Godot.Collections.Array` to end with `Collection`
- A few culture specifications and use of `AsSpan` instead of `SubString` in `StringExtensions`
- Disable CA1716 in GodotSharp

modules/mono/editor/Godot.NET.Sdk/Godot.SourceGenerators/MustBeVariantAnalyzer.cs

@@ -1,5 +1,4 @@
 using System.Collections.Immutable;
-using System.Diagnostics;
 using System.Linq;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
@@ -34,7 +33,7 @@ namespace Godot.SourceGenerators
 
             // Method invocation or variable declaration that contained the type arguments
             var parentSyntax = context.Node.Parent;
-            Debug.Assert(parentSyntax != null);
+            Helper.ThrowIfNull(parentSyntax);
 
             var sm = context.SemanticModel;
 
@@ -49,9 +48,10 @@ namespace Godot.SourceGenerators
                     continue;
 
                 var typeSymbol = sm.GetSymbolInfo(typeSyntax).Symbol as ITypeSymbol;
-                Debug.Assert(typeSymbol != null);
+                Helper.ThrowIfNull(typeSymbol);
 
                 var parentSymbol = sm.GetSymbolInfo(parentSyntax).Symbol;
+                Helper.ThrowIfNull(parentSymbol);
 
                 if (!ShouldCheckTypeArgument(context, parentSyntax, parentSymbol, typeSyntax, typeSymbol, i))
                 {
@@ -69,7 +69,7 @@ namespace Godot.SourceGenerators
 
                 var marshalType = MarshalUtils.ConvertManagedTypeToMarshalType(typeSymbol, typeCache);
 
-                if (marshalType == null)
+                if (marshalType is null)
                 {
                     Common.ReportGenericTypeArgumentMustBeVariant(context, typeSyntax, typeSymbol);
                     continue;