Clarify that minLines/maxLines affect the height of the field and not the number of lines that can be entered.

This reverts commit b9bf5769.

This fixes VisualDensity.effectiveConstraints to clamp to the max values of the constraint, instead of to double.infinity.

This removes the broken video for GestureDetector, and replaces it with a Dartpad sample, for both samples in GestureDetector.