add setU_itvob1 and setU_1itvob

[t6s]

Motivation for this change

fix #1914 by reintroducing old forms of setUitv1 and setU1itv (but under different names)

Checklist

• added corresponding entries in CHANGELOG_UNRELEASED.md

• added corresponding documentation in the headers

Reference: How to document

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• 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.

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