Fix viewport blanking after large programmatic scroll (setFrameSize re-entrance)

When `relocateViewport(to: docStart)` calls `setFrameSize(width, lineHeight)`
from a scrolled-down position, AppKit must synchronously retract the clip
view to fit the new bounds. That fires `prepareContent` from inside
`super.setFrameSize`, which calls `updateContentSizeIfNeeded` and re-enters
`setFrameSize` with the full document height. The recursive call correctly
resizes `contentView`. When control returns to the outer call, `newSize`
is still the original (small) value, and `contentView.frame.size = newSize`
stomps the recursive call's result.

End state: textView at full height, contentView and contentViewportView at
one-line height, fragment views past line 1 clipped. Manifests as
Cmd-End → Cmd-Home blanking the editor on a multi-screen word-wrapped
document. Resizing the window or toggling word-wrap restores rendering
because both go through a fresh non-re-entrant `setFrameSize`.

Fix: after `super.setFrameSize`, read `frame.size` (which reflects any
recursive resize) rather than the stale `newSize` parameter. When no
re-entrance occurred, `frame.size == newSize`, so the common path is
unchanged.

Author: iliasaz

Sources/STTextViewAppKit/STTextView.swift

@@ -1465,11 +1465,18 @@ open class STTextView: NSView, NSTextInput, NSTextContent, STTextViewProtocol {
     override open func setFrameSize(_ newSize: NSSize) {
         super.setFrameSize(newSize)
 
+        // `super.setFrameSize` can synchronously fire `prepareContent`, which
+        // may recursively call back into `setFrameSize` with a different
+        // size. In that case `self.frame.size` no longer matches `newSize`;
+        // use the current frame so we don't stomp the recursive call's
+        // result and leave `contentView` pinned to the intermediate size.
+        let effectiveSize = frame.size
+
         // contentView should always fill the entire STTextView
         contentView.frame.origin.x = gutterView?.frame.width ?? 0
-        contentView.frame.size = newSize
+        contentView.frame.size = effectiveSize
 
-        updateTextContainerSize(proposedSize: newSize)
+        updateTextContainerSize(proposedSize: effectiveSize)
 
         if inLayout {
             needsRelayout = true