chore(data/set/intervals): golf, rename (#12893)
* rename `set.mem_Ioo_or_eq_endpoints_of_mem_Icc` →
`set.eq_endpoints_or_mem_Ioo_of_mem_Icc`;
* rename `set.mem_Ioo_or_eq_left_of_mem_Ico` →
`set.eq_left_or_mem_Ioo_of_mem_Ico`;
* rename `set.mem_Ioo_or_eq_right_of_mem_Ioc` →
`set.eq_right_or_mem_Ioo_of_mem_Ioc`;
* golf the proofs of these lemmas.
The new names better reflect the order of terms in `or`.
