Add correct visible range calculation for TextKit 2 (#42)

* Add correct visible range calculation for TK2

* replace spaces with tabs

Sources/Neon/NSTextView+VisibleRange.swift

@@ -33,7 +33,16 @@ extension NSTextView {
 	}
 
 	public var visibleTextRange: NSRange {
-		return textRange(for: visibleRect)
+		guard
+			#available(macOS 12.0, *),
+			let textLayoutManager,
+			let viewportRange = textLayoutManager.textViewportLayoutController.viewportRange,
+			let textContentManager = textLayoutManager.textContentManager
+		else {
+			return textRange(for: visibleRect)
+		}
+
+		return NSRange(viewportRange, provider: textContentManager)
 	}
 }
 #endif