What's the proper name for the miscellaneous studs that are welded to various places - the most common being the pedal bracket in the engine compartment?

Ive always refereed to them as spin weld bolts / studs.

they have a ring or series of raised dots or a ring on the bottom side of the head. The head requires a special fixture to spin the bolt and the ridge or dots weld themselves to the surface due to extreme heat

That's Projection Spot Welding. But there is a welding technique that spin welds.

I wanted the name so I could see if there were any YouTube videos on how to easily remove them.

Pem studs, Weld studs, Projection stud...there are a few names and methods for mounting them initially with a quick weld dab to lock em in.

Studs: grip with a visegrip. Twist slightly in a circular manner. Back-Forth slightly. You should feel the weld "give" (but also maybe base metal). BUT: can't always be certain that base-metal won't "give-way". Of stud has larger dia. & metal thin: isn't tricky. Depends on how "sturdy" the weld is.