[Merged by Bors] - chore: classify porting notes about ext

[Vierkantor]

I checked all porting notes mentioning ext and either fixed them (see #17810), or classified them as

• Porting note: ext does not look through definitions, so we need more ext lemmas #5229 if it's a new @[ext] lemma
• Porting note: broken ext #11041 if it's a regression in ext
• Porting note: removed @[ext] #11182 if @[ext] had to be removed

This PR should contain only modifications to comments.

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[github-actions]

PR summary c102b349b6

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

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 🎉

bors merge

[mathlib-bors]

Pull request successfully merged into master.

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