Nether portals can be used to break through the bedrock floor in the nether

Nether portal generation can be exploited to make holes in the bedrock floor of the nether.

Reproduction:

1. Create a portal in the overworld as low as possible 
2. Set your spawnpoint next to the portal using a bed.
3. Teleport to the nether normally using the portal.
4. Completely clear the area around the portal location of non-bedrock blocks (see attached screenshot). This can be done using TNT in survival or via commands if cheats are enabled. This needs to be done to an area from the bottom bedrock barrier to the top bedrock barrier and about 50-100 blocks around the portal.
5. Destroy the portal in the nether and kill your character to teleport back to your bed next to the overworld portal
6. Enter your overworld portal
7. Repeat Step 5 and 6 until the portal has broken through the bedrock floor.

With every new portal generation, the portal will move one block down until it has broken through the bedrock floor.  According to my testing this can be done in 3-5 attempts most of the time. 

This also affects 1.16.5.