fix(linear_algebra/basic): fix incorrect namespaces (#8757)
Previously there were names in the `linear_map` namespace which were about `linear_equiv`s.
This moves:
* `linear_map.fun_congr_left` to `linear_equiv.fun_congr_left`
* `linear_map.automorphism_group` to `linear_equiv.automorphism_group`
* `linear_map.automorphism_group.to_linear_map_monoid_hom` to `linear_equiv.automorphism_group.to_linear_map_monoid_hom`
