WIP: Frobenius Elements

[tb65536]

This PR proves the existence of Frobenius elements in algebraic number theory.

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• [ ] depends on: #17752
• [ ] depends on: #17753
• [x] depends on: #17849
• [x] depends on: #18143
• [x] depends on: #18147
• [ ] depends on: #18148

[github-actions[bot]]

PR summary fe6333a207

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.NumberTheory.FrobeniusElement	1372

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Declarations diff

+ Ideal.Quotient.stabilizerHom_surjective + IsFractionRing.stabilizerHom + IsFractionRing.stabilizerHom_surjective + IsInvariant + charpoly + charpoly_coeff_smul + charpoly_eq + charpoly_eq_prod_smul + charpoly_eval + charpoly_mem_lifts + charpoly_monic + charpoly_smul + exists_smul_of_under_eq + isIntegral

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.

[mathlib4-dependent-issues-bot]

This PR/issue depends on:

• ~~leanprover-community/mathlib4#17752~~
• ~~leanprover-community/mathlib4#17753~~
• ~~leanprover-community/mathlib4#17849~~
• ~~leanprover-community/mathlib4#18143~~
• ~~leanprover-community/mathlib4#18147~~
• ~~leanprover-community/mathlib4#18148~~
• ~~leanprover-community/mathlib4#18241~~
• ~~leanprover-community/mathlib4#18355~~
• ~~leanprover-community/mathlib4#18560~~
• ~~leanprover-community/mathlib4#18562~~
• ~~leanprover-community/mathlib4#18594~~
• ~~leanprover-community/mathlib4#18703~~ By Dependent Issues (🤖). Happy coding!

[tb65536]

Abandoned in favor of #19926.