[Merged by Bors] - chore(Data/Nat/Notation): move Init/Data/Nat/Notation

[jcommelin]

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[github-actions]

PR summary ba28532919

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

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>

[grunweg]

Looks good, thanks!
maintainer merge

[github-actions]

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

[kim-em]

bors merge

[urkud]

Looks like this conflicts with #14762. Please merge them in some order.
bors r-
bors d+

[mathlib-bors]

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

[mathlib-bors]

Canceled.

[jcommelin]

bors r+

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

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