[Merged by Bors] - refactor: move the definition of IsRegular earlier

[eric-wieser]

The motivation here is to be able to define things like IsCancelMulZero in terms of IsRegular, which would allow API for the latter to be used to provide instances for the former.

As a first step, this moves the MulZeroClass lemmas abut IsRegular into the GroupWithZero folder, which is consistent with the ring lemmas living inside the Ring folder.

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[github-actions]

PR summary f609d6347c

Import changes for modified files

Dependency changes

File	Base Count	Head Count	Change
Mathlib.Algebra.Regular.Basic	214	120	-94 (-43.93%)
Mathlib.Algebra.Ring.Regular	219	135	-84 (-38.36%)
Mathlib.Algebra.Order.Monoid.Unbundled.Basic	208	212	+4 (+1.92%)

Import changes for all files

Files	Import difference
There are 4371 files with changed transitive imports taking up over 191168 characters: this is too many to display!
You can run scripts/import_trans_difference.sh all locally to see the whole output.

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Declarations diff

+ isLeftRegular
- MulLECancellable.isLeftRegular

You can run this locally as follows

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

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

The doc-module for script/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/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).

[YaelDillies]

Thanks!

maintainer delegate

[github-actions]

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

[jcommelin]

Thanks 🎉

bors merge

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

• CI Success