fix itvbc, etc. naming

[affeldt-aist]

Motivation for this change

This PR removes the deprecations on measurable_fun_itv_co and measurable_fun_itv_oc
and instead renames them following the naming convention from set_interval.v (PR 1935).

It also renames a couple of similarly-named lemmas.

Checklist

• added corresponding entries in CHANGELOG_UNRELEASED.md

• added corresponding documentation in the headers

Reference: How to document

Merge policy

As a rule of thumb:

• PRs with several commits that make sense individually and that
  all compile are preferentially merged into master.
• PRs with disorganized commits are very likely to be squash-rebased.

Reminder to reviewers

• Read this Checklist
• Put a milestone if possible
• Check labels

[t6s]

The new names look more consistent and solid.

[affeldt-aist]

Yes, it indeed feels better. Thanks for your time on Wednesday!