Add extension to NSTextLayoutFragment for isExtraLineFragment property

This commit introduces a new extension to NSTextLayoutFragment, adding a
computed property that checks if any of its text line fragments are
considered extra line fragments. This functionality enhances text layout
manipulation by providing an easy way to identify extra lines.

Sources/STTextViewCommon/Extensions/NStextLayoutFragment+isExtraLineFragment.swift

@@ -0,0 +1,15 @@
+//  Created by Marcin Krzyzanowski
+//  https://github.com/krzyzanowskim/STTextView/blob/main/LICENSE.md
+
+#if canImport(AppKit) && !targetEnvironment(macCatalyst)
+import AppKit
+#endif
+#if canImport(UIKit)
+import UIKit
+#endif
+
+extension NSTextLayoutFragment {
+    package var isExtraLineFragment: Bool {
+        textLineFragments.contains(where: \.isExtraLineFragment)
+    }
+}