chore(LinearAlgebra/Matrix): deprecate Matrix.star_mul

[Vierkantor]

This PR generalizes the Matrix.starMul instance so that Matrix.star_mul can be replaced with star_mul from the root namespace. I verified the two are exactly the same (after this generalization) by with_reducible rfl. I noticed this while looking at docstrings.

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[github-actions]

PR summary cc26c21489

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

+ instance [Fintype n] [NonUnitalNonAssocSemiring α] [StarRing α] : StarRing (Matrix n n α)
- instance [Fintype n] [NonUnitalSemiring α] [StarRing α] : StarRing (Matrix n n α)

You can run this locally as follows

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

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

The doc-module for scripts/pr_summary/declarations_diff.sh contains some details about this script.

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No changes to technical debt.

You can run this locally as

./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).

[themathqueen]

maintainer merge

[github-actions]

🚀 Pull request has been placed on the maintainer queue by themathqueen.

[j-loreaux]

bors merge

[mathlib-bors]

Merge conflict.

Merge or rebase master into this PR and resolve the conflict, then someone with permission can run bors r+ or bors retry.

[mathlib-merge-conflicts]

This pull request has conflicts, please merge master and resolve them.