feat(SymbolicDynamics): add monotonicity lemma for LanguageOn

[Sfgangloff]

In Symbolic dynamics.

Proof that the language of a set of configurations is monotone with respect to inclusion of configuration sets:

X ⊆ Y → LanguageOn X U ⊆ LanguageOn Y U

The proof is a direct unfolding of definitions: a pattern in the language of X comes from restricting some configuration x ∈ X, and inclusion X ⊆ Y allows the same witness to be used for Y.

[github-actions]

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[github-actions]

PR summary 834e51690b

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

+ isMonotone_LanguageOn

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.

---

No changes to strong technical debt.

No changes to weak technical debt.

[github-actions]

✅ PR Title Formatted Correctly

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