Add contentFrame public property to STTextView

Add a public contentFrame property to STTextView on both AppKit and UIKit that
exposes the frame of the contentView. This allows external code to access the
frame of the text view's content.

Author: krzyzanowskim

Sources/STTextViewAppKit/STTextView.swift

@@ -430,6 +430,11 @@ import AVFoundation
     /// Content view. Layout fragments content.
     internal let contentView: STContentView
 
+    /// Content frame. Layout fragments content frame.
+    public var contentFrame: CGRect {
+        contentView.frame
+    }
+
     /// Selection highlight content view.
     internal let selectionView: STSelectionView
 

Sources/STTextViewUIKit/STTextView.swift

@@ -183,6 +183,11 @@ import STTextViewCommon
     /// Content view. Layout fragments content.
     internal let contentView: STContentView
 
+    /// Content frame. Layout fragments content frame.
+    public var contentFrame: CGRect {
+        contentView.frame
+    }
+
     /// Line highlight view.
     internal let lineHighlightView: STLineHighlightView