chore(analysis): move lemmas around (#12621)
* move `smul_unit_ball` to `analysis.normed_space.pointwise`, rename it to `smul_unit_ball_of_pos`;
* reorder lemmas in `analysis.normed_space.pointwise`;
* add `vadd_ball_zero`, `vadd_closed_ball_zero`, `smul_unit`, `affinity_unit_ball`, `affinity_unit_closed_ball`.
Co-authored-by: Yaël Dillies <yael.dillies@gmail.com>
