[Merged by Bors] - feat(Logic/Function/Basic) : lemmas about composition of and in onFun

[Hagb]

(f.onFun g).onFun h = f.onFun (g ∘ h) and its symmetric variant.

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It was a lemmas for #39781, which has been closed since there would be a better proof.

[github-actions]

PR summary 6d6f20866d

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

+ onFun_comp_eq
+ onFun_onFun_eq

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

## summary with just the declaration names:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

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No changes to strong technical debt.

No changes to weak technical debt.

[b-mehta]

Thanks!

bors merge

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

• ci (staging) / Lint style
• ci (staging) / Post-Build Step
• ci (staging) / Build
• ci (staging) / Post-CI job