How do I warp to the original dimension in the 20w14infinite snapshot of Minecraft Java Edition?

All the numerical dimension IDs (which all text input to /warp gets converted to, that's why /warp overworld doesn't work) are for either a randomly generated dimension or one of the easter egg dimensions. Overworld, Nether and End are not accessible this way.

You can use /execute in overworld run tp @s ~ ~ ~, but be careful, this puts you at the coordinates you currently are, but in the Overworld, it does not select a proper spawning location for you. You could use /spreadplayers (archive), but even that behaves differently from /warp (for example if you use it in the Nether, it puts you on top of the bedrock roof).

Using execute in <dimension> will run the command in that dimension. Therefore, the way to the return to the overworld:

/execute in minecraft:overworld run tp @s 0 100 0

Or if you know a set of coordinates in the OW, you can teleport there.