Clay generation similar to current gravel and dirt underground.

Title speaks for itself, we should have clay generate underground the same way that gravel, dirt, andesite, etc generates underground. That being small pockets surrounded by stone. This would make clay and bricks a far more accessible building material. I assume this could be done by adding it to the list of blocks that generate in that way since they all seem to generate the same way.

This would be a huge help and give the ability to use bricks and clay far more often in builds. Right now, it is EXTREMELY limited as it only spawns in rivers and lakes, which aren't too common.