Add section: cdf of lebesgue stieltjes measure

[Yosuke-Ito-345]

Motivation for this change

I add Section cdf_of_lebesgue_stieltjes_mesure in probability.v, which proves that the cumulative distribution function of a Lebesgue-Stieltjes measure goes back to the underlying function.

Checklist

• added corresponding entries in CHANGELOG_UNRELEASED.md

• added corresponding documentation in the headers

Reference: How to document

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[Yosuke-Ito-345]

This error is strange.

Error: The variable truncn was not found in the current environment.

Why was truncn not found? I can certainly find truncn in archimedean.v.

[affeldt-aist]

This error is strange.

Error: The variable truncn was not found in the current environment.

Why was truncn not found? I can certainly find truncn in archimedean.v.

It might be because the CI is testing with the previous version of MathComp (2.3.0) in which there was no truncn.

[Yosuke-Ito-345]

Thank you for the comment.
Then I think the pull request went well, but please tell me if I need to fix something.