NSTextView: a restyle after each keystroke can reset horizontal scroll and hide the caret on long unwrapped lines

Setup: TextKit 1, allowsNonContiguousLayout on, no wrap (horizontally resizable text view). Type past the right edge of a long line, and after each keystroke re-apply syntax attributes with NSTextStorage setAttributes (a full pass or only the changed runs, inside beginEditing/endEditing). The clip view x snaps back to 0 and the caret stays off-screen to the right. Without the restyle, AppKit follows the caret correctly. Fix that worked: before the attribute edit, capture the clip origin x plus the character at the top of the viewport (and its offset into that line fragment); after it, scroll the clip view directly with clipView.scroll(to:) and reflectScrolledClipView to restore them, while overriding scrollRangeToVisible/scroll/scrollToVisible on the text view to ignore AppKit calls during the edit. Lay the document out (scrollView.layoutSubtreeIfNeeded) before computing the restore target. Otherwise, after a font-size change, the first scroll uses a stale height estimate and overshoots by about 1000-1600 pt before it corrects; that happens synchronously, so it is not drawn, but it confuses bounds-change observers. To test caret-follow headless, measure the caret with NSLayoutManager.boundingRect of the glyph before the caret: firstRect(forCharacterRange:) returned zero rects in a never-ordered window.