tiny_skia: apply clip_mask to shadows

[B0ney]

I found that the shadow rendering code isn't using the clip bounds properly. leading to some artifacting.

Here's demo (I've modified the styling to show the shadows).

Without clip_mask

With clip_mask

Note that the text is still overwriting the shadows (for both cases). But I think this should get us closer :)

[T-256]

LGTM, and sorry for late response, I didn't enable notification for this repo.

[T-256]

With example at here I still get a little out of bounds shadows:

[B0ney]

I'll have another look at it.

[B0ney]

I've made another pr here: #2

I think that should finally solve the issue?