I am not a lawyer, but from my understanding the legal precedent is NEC v. Intel which established that clean-room software development is not infringing, even if it performs the same functionality as the original.

As an aside, this clean room engineering is one of the plot points of Season 1 of the TV show Halt and Catch Fire where the fictional characters do this with the BIOS image they dumped.

Sure. The reimplementation of the IBM PC BIOS that gave birth to IBM Compatibles is the canonical example.

Yes. Compaq's reverse engineering of the IBM PC BIOS set the precedent.

It is the reason AMD exists.