Moved NSRange clamped(_:) extension to common package

The NSRange clamped(_:) extension was moved from the
STTextViewAppKit/STTextView+NSTextCheckingClient.swift file to a new file
STTextViewCommon/Extensions/NSRange+Helpers.swift in the common package so it
can be shared between different packages.

Author: krzyzanowskim

Sources/STTextViewAppKit/STTextView+NSTextCheckingClient.swift

@@ -329,15 +329,3 @@ extension STTextView: NSIgnoreMisspelledWords {
     }
 
 }
-
-private extension NSRange {
-    func clamped(_ limits: NSRange) -> Self? {
-        guard let limits = Range(limits),
-              let clampedRange = Range(self)?.clamped(to: limits)
-        else {
-            return nil
-        }
-
-        return Self(clampedRange)
-    }
-}

Sources/STTextViewCommon/Extensions/NSRange+Helpers.swift

@@ -0,0 +1,14 @@
+import Foundation
+
+package extension NSRange {
+    func clamped(_ limits: NSRange) -> Self? {
+        guard let limits = Range(limits),
+              let clampedRange = Range(self)?.clamped(to: limits)
+        else {
+            return nil
+        }
+
+        return Self(clampedRange)
+    }
+}
+