Request a layout when a paragraph's overflow mode is changed (#9485)

A change in overflow mode requires calculation of the text size and resetting
the overflow shader

packages/flutter/lib/src/rendering/paragraph.dart

@@ -98,7 +98,7 @@ class RenderParagraph extends RenderBox {
       return;
     _overflow = value;
     _textPainter.ellipsis = value == TextOverflow.ellipsis ? _kEllipsis : null;
-    markNeedsPaint();
+    markNeedsLayout();
   }
 
   /// The number of font pixels for each logical pixel.

packages/flutter/test/rendering/paragraph_test.dart

@@ -140,6 +140,10 @@ void main() {
     relayoutWith(maxLines: 3, softWrap: true, overflow: TextOverflow.fade);
     expect(paragraph.debugHasOverflowShader, isTrue);
 
+    // Change back to ellipsis and check that the fade shader is cleared.
+    relayoutWith(maxLines: 3, softWrap: true, overflow: TextOverflow.ellipsis);
+    expect(paragraph.debugHasOverflowShader, isFalse);
+
     relayoutWith(maxLines: 100, softWrap: true, overflow: TextOverflow.fade);
     expect(paragraph.debugHasOverflowShader, isFalse);
   });