widget: use byte length when comparing with caret position

Fixes misaligned carets when the Editor text contains code points
represented by multiple UTF-8 bytes. Line lengths should be
measured in bytes instead of glyphs for caret positioning.

Signed-off-by: tainted-bit <sourcehut@taintedbit.com>

widget/editor.go

@@ -483,7 +483,7 @@ loop:
 		l := e.lines[carLine]
 		y += (prevDesc + l.Ascent).Ceil()
 		prevDesc = l.Descent
-		if carLine == len(e.lines)-1 || idx+len(l.Layout) > e.rr.caret {
+		if carLine == len(e.lines)-1 || idx+l.Len > e.rr.caret {
 			for _, g := range l.Layout {
 				if idx == e.rr.caret {
 					break loop