feat(Algebra/Group/Subgroup, GroupTheory/QuotientGroup): strengthen second isomorphism theorem for groups

[jhanschoo]

The stronger statement is necessary when we wish that H and H ⊔ N in the statement _ ⧸ N.subgroupOf H ≃* _ ⧸ N.subgroupOf (H ⊔ N) may need to be of a type larger than whichever subgroup H is normal in. Furthermore, this commit adapts some basic results about Normal subgroups to be wrt subgroups of normalizers instead.

Moves:

• Subgroup.le_normalizer_of_normal -> Subgroup.le_normalizer_of_normal_subgroupOf

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The primary reason for introducing this variation is that the existing formulation becomes a pain when quotienting subnormal groups. So suppose my ambient group is G and my normalizer is T : Subgroup G, the result I can get from the existing formulation is something like _ ⧸ (N : T).subgroupOf (H : T) ≃* _ ⧸ (N : T).subgroupOf (H ⊔ N : T), and it is difficult or tedious to recover the desired statement _ ⧸ N.subgroupOf H ≃* _ ⧸ N.subgroupOf (H ⊔ N) from it.

[github-actions]

PR summary a90a44f49c

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

+ inf_subgroupOf_normal_of_le_normalizer
+ le_normalizer_mul
+ le_normalizer_of_normal'
+ le_normalizer_of_normal_subgroupOf
+ mul_le_normalizer
+ quotientInfEquivProdNormalizerQuotient
+ setNormalizer_normalizer
+ set_mul_normalizer_comm
+ subgroupOf_sup_normal_of_le_normalizer
+ subset_normalizer_of_normal

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.

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No changes to technical debt.

You can run this locally as

./scripts/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).