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/ScriptMethodsGenerator.cs

@@ -144,7 +144,7 @@ namespace Godot.SourceGenerators
                 .Append("    /// </summary>\n");
 
             source.Append(
-                $"    public new class MethodName : {symbol.BaseType.FullQualifiedNameIncludeGlobal()}.MethodName {{\n");
+                $"    public new class MethodName : {symbol.BaseType!.FullQualifiedNameIncludeGlobal()}.MethodName {{\n");
 
             // Generate cached StringNames for methods and properties, for fast lookup