Continuity of Rintegral in its bounds

[nmolinamounier]

Motivation for this change

Split from #2023. Depends on #2029, #2037 and #2039.

Proves that the real integral is a continuous function in its bounds, with only an integrability hypothesis.

Checklist

• added corresponding entries in CHANGELOG_UNRELEASED.md
• Merge normed module identity convergence lemmas #2029
• Merge Rintegral manipulation lemmas #2037
• Merge Dominated convergence for Rintegral #2039

• 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.

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• Read this Checklist
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[nmolinamounier]

Closing because I will soon have a much cleaner statement and proof based on #2126.