Validate code tags for class and member references

This commit also adds means to manually disable warnings
in `code` tags where it's a false positive with the new
`skip-lint` attribute.

Warnings are now enabled on CI to prevent future errors.

doc/classes/Variant.xml

@@ -28,7 +28,7 @@
 		[/codeblocks]
 		Godot tracks all scripting API variables within Variants. Without even realizing it, you use Variants all the time. When a particular language enforces its own rules for keeping data typed, then that language is applying its own custom logic over the base Variant scripting API.
 		- GDScript automatically wrap values in them. It keeps all data in plain Variants by default and then optionally enforces custom static typing rules on variable types.
-		- C# is statically typed, but uses its own implementation of the [code]Variant[/code] type in place of Godot's Variant class when it needs to represent a dynamic value. A [code]Variant[/code] can be assigned any compatible type implicitly but converting requires an explicit cast.
+		- C# is statically typed, but uses its own implementation of the Variant type in place of Godot's [Variant] class when it needs to represent a dynamic value. C# Variant can be assigned any compatible type implicitly but converting requires an explicit cast.
 		The global [method @GlobalScope.typeof] function returns the enumerated value of the Variant type stored in the current variable (see [enum Variant.Type]).
 		[codeblocks]
 		[gdscript]