chore: add missing additive deprecation aliases for #37793

[kbuzzard]

See #mathlib4 > #37793 and `to_additive` @ 💬 . Generated by Claude code but manually reviewed by me.

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[github-actions]

PR summary 6770747912

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

+ AddMonoidHom.coe_finset_sum
+ AddMonoidHom.finset_sum_apply
+ FS.finset_sum
+ Filter.map_atTop_finset_sum_le_of_sum_eq
+ Function.Injective.map_atTop_finset_sum_eq
+ alternatingSum_eq_finset_sum
+ contMDiffAt_finset_sum
+ contMDiffAt_finset_sum'
+ contMDiffOn_finset_sum
+ contMDiffOn_finset_sum'
+ contMDiffWithinAt_finset_sum
+ contMDiffWithinAt_finset_sum'
+ contMDiff_finset_sum
+ contMDiff_finset_sum'
+ continuousOn_finset_sum
+ continuous_finset_sum
+ exists_norm_finset_sum_le
+ exists_norm_finset_sum_le_of_nonempty
+ finset_sum'
+ finset_sum_mem_finset_sum
+ finset_sum_singleton
+ finset_sum_subset_finset_sum
+ finsum_eq_finset_sum_of_support_subset
+ iCondIndepFun.condIndepFun_finset_sum_of_notMem
+ image_finset_sum
+ image_finset_sum_pi
+ map_finset_sum
+ mem_finset_sum
+ tendsto_finset_sum
++ finset_sum
++ iIndepFun.indepFun_finset_sum_of_notMem
++ iIndepFun.indepFun_finset_sum_of_notMem₀
++ sum_finset_sum_index

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

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

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

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No changes to technical debt.

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/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).

[kbuzzard]

Hmm, apparently I should be following the pattern at #38550 but I'm out of credits for now. Will come back to this in about 10 hours.