Mask
**Describe the requested icon(s)**

I'm making a graphics application (so, I'd love to see a lot more of these!) and usually, you can add a "mask" in typical graphics applications, such as Photoshop, Affinity, or Gimp. It's just a rounded rectangle or square with a circle inside. I tried searching Phosphor for squares and circles, but alas, no overlap with the two.

**References**

You can see the icon here:
https://community.adobe.com/t5/image/serverpage/image-id/68506i6A244AB5C6F04FF7/image-size/large?v=v2&px=999

**Additional context**

It is for creating a partly opaque layer, where the masked part is invisible and the unmasked part is opaque.
