Someone
Adventurer
I'd say not in core. Frankly I don't think they have a place in magical fantasy, it is a sci-fi trope. In a fantasy game they are just spell casters with a different backstory IMO.
In other mythologies I’ve found examples of enlightened people with capabilities very similar to what we understand as psionics; they almost always are spiritual people and could be classified as priests, but the supernatural feats they are capable of are described as result of their superior understanding of the universe, not as intervention from divine beings so I don't quite agree it's a sci-fi trope as much as fireball being called "spherical plasma detonation" makes magic sci-fi.
In any case, they do not fit the standard western fantasy settings and if 5e wants to stick to that then it shouldn’t be core. However I hope there’s at least to “fake” it in core and there are ways to play a mage eschewing spellbook and somatic/verbal components, and enough of the thematically appropriate spells.