[css-ui-4] Show end-of-line carets even if they overflow

See #10289

Author: frivoal

css-ui-4/Overview.bs

@@ -1332,6 +1332,13 @@ Shape of the insertion caret: 'caret-shape'</h4>
 	the caret remains visible even if it has been scaled down
 	via means such as transformations [[CSS-TRANSFORMS-1]].
 
+	When there is not enough room at the end of a line
+	to display the caret positioned there,
+	the user agents should still display it,
+	even if that means means painting
+	past the bounds of the [=scrollable overflow area=];
+	user agents may impose limits on this and clip as necessary.
+
 	The stacking position of the caret is left undefined within the following constraints:
 
 	<ul>