Add support for web

[wreppun]

Flutter does not currently support either:

• BlendMode.clear
• Path.combine

To work around this, I swapped out the layered approach in the current repo with an approach which simply draws the inverted shape (either a circle, rectangle, or rounded rectangle) used for the overlay.

It would be nice if Flutter Web supported the above listed method. But they don't and I need this now, so I thought I'd open a PR if you're interested. It ain't pretty, but it works.

Cheers.

[RafaelBarbosatec]

Hi @wreppun !
Thanks so much for contribution !!!!
It’s awesome !
I just encountered a small problem when the animation is rectangle type. notice in the video that in the exit animation it doesn't complete the animation until it leaves the screen completely.

Gravacao.de.Tela.2021-07-27.as.13.09.26.mov

[RafaelBarbosatec]

Thanks for contributing !! LGTM!
I will make the necessary adjustments to fix this little bug!