[Merged by Bors] - chore: split Data.Set.Basic

[kim-em]

Delay imports of Data.Order.SymmDiff, as many things downstream don't need it.

[github-actions]

PR summary 4d877d4c3c

Import changes for modified files

Dependency changes

File	Base Count	Head Count	Change
Mathlib.Data.Set.Basic	213	194	-19 (-8.92%)
Mathlib.Data.SetLike.Basic	216	197	-19 (-8.80%)
Mathlib.Order.Filter.Defs	216	197	-19 (-8.80%)
Mathlib.Order.Interval.Set.Basic	220	202	-18 (-8.18%)
Mathlib.Data.PEquiv	217	200	-17 (-7.83%)
Mathlib.Algebra.Group.Center	233	215	-18 (-7.73%)
Mathlib.Data.Set.Enumerate	333	332	-1 (-0.30%)
Mathlib.Data.PNat.Basic	422	421	-1 (-0.24%)

Import changes for all files

Files	Import difference
There are 4202 files with changed transitive imports taking up over 177914 characters: this is too many to display!
You can run scripts/import_trans_difference.sh all locally to see the whole output.

---

Declarations diff

No declarations were harmed in the making of this PR! 🐙

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.

[jcommelin]

Thanks 🎉

If CI passes, please remove the label awaiting-CI and merge this yourself, by adding a comment bors r+.

bors d+

[mathlib-bors]

✌️ kim-em can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

[kim-em]

bors merge

[mathlib-bors]

Pull request successfully merged into master.

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