Allow markdown to be selectable

[robert-virkus]

Is your feature request related to a problem? Please describe.
On Flutter Web I would like to allow users to select text

Describe the solution you'd like
Wrapping a MarkdownWidget in a SelectionArea should ideally allow users to select text.

Describe alternatives you've considered
Not sure if I could possibly override the BlockPainter builder to achieve it?

Additional context
Great work and happy new year!

[Sasha071201]

I need this as well. In my case, allowing text selection in MarkdownWidget is important, especially on Flutter Web. It would be great if wrapping it with SelectionArea worked out of the box.