feat: lemmas about HasLaw

[mathlib-splicebot]

The law of a random variable is given by the push-forward measure.
Lemmas related to integration.

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This PR was automatically created from PR #42999 by @EtienneC30 via a review comment by @EtienneC30.

[github-actions]

PR summary 3dac25aae5

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 (regex)

+ HasLaw.integrable
+ HasLaw.integrable_comp
+ HasLaw.memLp
+ HasLaw.memLp_comp
+ hasLaw_map

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 -- unavailable)

⚠️ No declarations diff yet: there is no built master snapshot at this PR's merge-base (typically a bors-batch intermediate that CI never built). Merge master into this PR and push to refresh.

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No changes to strong technical debt.

No changes to weak technical debt.

Current commit 3dac25aae5
Reference commit 1f29011071

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).