feat: prepare for removing @[simp] from Sum.forall and Sum.exists

[kim-em]

I would like to remove @[simp] from Sum.forall and Sum.exists, per leanprover/lean4#5900.

The right hand sides of these lemmas are more complicated, and moreover they cause many problems with simp lemma confluence. (Confluence tool coming soon!)

This PR pre-emptively prepares Mathlib for this change. If we can't get it review in time I can just make these lemmas into simp lemmas globally in Mathlib.

[github-actions]

PR summary e87de0c017

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

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

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./scripts/declarations_diff.sh long <optional_commit>

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