measure induced by a measurable function

[affeldt-aist]

Motivation for this change

This PR introduces a definition of measure induced by a measurable function,
similarly to the notion of signed measure induced by an integrable function in radon_nikodym.v.
The code is essentially coming from PR #2116 as one step towards its review.
It is used twice in PR #2116, hence justifying this PR.

fyi: @lyonel2017

Checklist

• added corresponding entries in CHANGELOG_UNRELEASED.md

• added corresponding documentation in the headers

Reference: How to document

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