Change Portal blocks to be non-solid

One thing that doesn't make too much sense is portal blocks having a hitbox. I feel like the portal blocks should have the same properties as liquids where you can place/break blocks through them and not be able to hit them (they're indestructible anyways). This would improve a variety of things, such as being able to place blocks on the other side of a portal without going around or breaking it, and also not getting trapped in a portal when someone places blocks on either side.