Ensure that SelectionArea box height matches the text height

[walsha2]

Right now using SelectionArea the selected text does not account for the height property and in turn the selected region has gaps:

[walsha2]

This is actually not possible in Flutter using SelectionArea just yet. There is no way to set selectionHeightStyle for a SelectionArea or in TextSelectionThemeData.

Ideal Result

The way to get this to work is using SelectableText directly because it exposes a selectionHeightStyle option:

SelectableText(
  "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.",
  selectionHeightStyle: ui.BoxHeightStyle.includeLineSpacingTop,
),

[walsha2]

Related Flutter issue:

• SelectionArea should expose a selectionHeightStyle option flutter/flutter#161010