go.*,text: implement shaper-driven line truncation

This commit pushes limiting the maximum number of lines of text into
the shaper implementation. This is more efficient than doing it in
widgets, and also opens the door for future use of the shaper to
insert ellipsis and other truncating characters as appropriate.

I realized that we lost the implementation of limiting the number of
lines of text in my text stack overhaul, so this fixes a regression
from that work.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

text/shaper.go

@@ -192,6 +192,8 @@ func (l *Shaper) layoutText(params Parameters, minWidth, maxWidth int, lc system
 		l.txt.append(l.layoutParagraph(params, minWidth, maxWidth, lc, "", nil))
 		return
 	}
+	truncating := params.MaxLines > 0
+	maxLines := params.MaxLines
 	var done bool
 	var startByte int
 	var endByte int
@@ -222,6 +224,12 @@ func (l *Shaper) layoutText(params Parameters, minWidth, maxWidth int, lc system
 			done = endByte == len(str)
 		}
 		l.txt.append(l.layoutParagraph(params, minWidth, maxWidth, lc, str[startByte:endByte], l.paragraph))
+		if truncating {
+			params.MaxLines = maxLines - len(l.txt.lines)
+			if params.MaxLines == 0 {
+				done = true
+			}
+		}
 		if done {
 			return
 		}