textLayoutRangeView: Fix layout calculation and image drawing

Calculate the frame of the text range more accurately, taking into account
the padding and margins of each text layout fragment.

Simplify the image() function to call stImage() directly.

When drawing, calculate the origin for each text line fragment based on the
layout fragment frame origin, rather than always starting at .zero.

Sources/STTextViewAppKit/STTextLayoutRangeView.swift

@@ -30,10 +30,10 @@ open class STTextLayoutRangeView: NSView {
         var frame: CGRect = textLayoutManager.textSegmentFrame(in: self.textRange, type: .standard)!
         textLayoutManager.enumerateTextLayoutFragments(in: self.textRange) { textLayoutFragment in
             frame = CGRect(
-                x: min(frame.origin.x, textLayoutFragment.layoutFragmentFrame.origin.x),
-                y: frame.origin.y,
-                width: max(frame.size.width, textLayoutFragment.renderingSurfaceBounds.width),
-                height: max(frame.size.height, textLayoutFragment.renderingSurfaceBounds.height)
+                x: min(frame.origin.x, textLayoutFragment.layoutFragmentFrame.minX),
+                y: min(frame.origin.y, textLayoutFragment.layoutFragmentFrame.minY),
+                width: max(frame.size.width, textLayoutFragment.layoutFragmentFrame.maxX + textLayoutFragment.leadingPadding + textLayoutFragment.trailingPadding),
+                height: max(frame.size.height, textLayoutFragment.layoutFragmentFrame.maxY + textLayoutFragment.topMargin + textLayoutFragment.bottomMargin)
             )
             return true
         }
@@ -47,26 +47,17 @@ open class STTextLayoutRangeView: NSView {
     }
 
     open func image() -> NSImage? {
-        guard let imageRep = bitmapImageRepForCachingDisplay(in: bounds) else {
-            return nil
-        }
-        cacheDisplay(in: bounds, to: imageRep)
-
-        guard let cgImage = imageRep.cgImage else {
-            return nil
-        }
-
-        return NSImage(cgImage: cgImage, size: bounds.size)
+        stImage()
     }
 
     open override func draw(_ dirtyRect: NSRect) {
         guard let ctx = NSGraphicsContext.current?.cgContext else { return }
 
-        var origin: CGPoint = .zero
         textLayoutManager.enumerateTextLayoutFragments(in: textRange) { textLayoutFragment in
             // at what location start draw the line. the first character is at textRange.location
             // I want to draw just a part of the line fragment, however I can only draw the whole line
             // so remove/delete unnecessary part of the line
+            var origin = textLayoutFragment.layoutFragmentFrame.origin
             for textLineFragment in textLayoutFragment.textLineFragments {
                 guard let textLineFragmentRange = textLineFragment.textRange(in: textLayoutFragment) else {
                     continue