feat(MeasureTheory/MeasurableSpace/Basic): add map_comap_eq_of_surjective and measurable_comap_iff_right

[teorth]

We have nine map_comap_eq_of_surjective lemmas for Submonoid, Subgroup, Subring, etc., but were lacking one for MeasurableSpace. This PR adds the analogous lemma; as an application it also establishes a dual version of measurable_comap_iff involving composition on the right rather than the left.

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Note: I have no applications in mind for this PR, so it can be considered low priority.

Discussed on Zulip here.

[github-actions]

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[github-actions]

PR summary 99ec11027c

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff (regex)

+ map_comap_eq_of_surjective
+ measurable_comap_iff_right

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.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit 99ec110).

• +2 new declarations
• −0 removed declarations

+MeasurableSpace.map_comap_eq_of_surjective
+measurable_comap_iff_right

---

No changes to strong technical debt.

No changes to weak technical debt.

Current commit 99ec11027c
Reference commit 005f0aa67b

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[github-actions]

✅ PR Title Formatted Correctly

The title of this PR has been updated to match our commit style conventions.
Thank you!

[plp127]

We don't want to be using apply where one of the _ holes becomes a new goal, see #mathlib4 > linter requests @ 💬
While we're here, let's also merge in the next line intro S hS as well

Suggested change

	apply le_antisymm _ le_map_comap
	intro S hS
	refine le_antisymm (fun S hS => ?_) le_map_comap

[plp127]

Suggested change

	simp only [measurable_iff_comap_le, ← comap_comp]
	refine ⟨ comap_mono, fun h ↦ ?_ ⟩
	simpa only [map_comap_eq_of_surjective hg] using map_mono (f := g) h
	rw [measurable_iff_le_map, measurable_iff_le_map, ← map_comp, map_comap_eq_of_surjective hg]