text,widget: remove fractional line height

The previous logic kept the y offset of a line as a fractional value
until the last possible moment in an effort to be as true to a fractional
line height as possible (minimize the error), but this interacts pathologically
with multi-line text selections, as the selections may have visibly different
gaps between lines. It's better to always shift lines by a fixed quantity of
whole pixels, even if it is technically less accurate to the desired line height.

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

text/gotext.go

@@ -513,12 +513,12 @@ func calculateYOffsets(lines []line) {
 	}
 	// Ceil the first value to ensure that we don't baseline it too close to the top of the
 	// viewport and cut off the top pixel.
-	currentY := fixed.I(lines[0].ascent.Ceil())
+	currentY := lines[0].ascent.Ceil()
 	for i := range lines {
 		if i > 0 {
-			currentY += lines[i].lineHeight
+			currentY += lines[i].lineHeight.Round()
 		}
-		lines[i].yOffset = currentY.Round()
+		lines[i].yOffset = currentY
 	}
 }