feat(analysis/normed_space): add Mazur-Ulam theorem (#2214)
Based on a proof by Jussi Väisälä, see [journal version](https://www.jstor.org/stable/3647749) or [preprint on web.archive](https://web.archive.org/web/20180516125105/http://www.helsinki.fi/~jvaisala/mazurulam.pdf).
Also rename `reflection` to `point_reflection` as was suggested by @rwbarton and @PatrickMassot
