fix: toggle debit credit amounts for transaction currency too; minor refactor (backport #44263)

[mergify]

Fixes: #44197 (comment)

Issue

Amount in transaction currency is -ve and on credit side.

• Ensures amount is transaction currency is updated consistently like amount in account currency
• Refactor, cleaner code with reduced duplication

  ---

  This is an automatic backport of pull request fix: toggle debit credit amounts for transaction currency too; minor refactor #44263 done by Mergify.

[mergify]

Cherry-pick of 8e759c3 has failed:

On branch mergify/bp/version-14-hotfix/pr-44263
Your branch is up to date with 'origin/version-14-hotfix'.

You are currently cherry-picking commit 8e759c32c4.
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Unmerged paths:
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	both modified:   erpnext/accounts/general_ledger.py

no changes added to commit (use "git add" and/or "git commit -a")

Cherry-pick of a10e175 has failed:

On branch mergify/bp/version-14-hotfix/pr-44263
Your branch is ahead of 'origin/version-14-hotfix' by 1 commit.
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You are currently cherry-picking commit a10e175bc9.
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  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   erpnext/accounts/doctype/journal_entry/test_journal_entry.py

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[vorasmit]

Transaction currency doesn't exist in v14 and hence this PR may not be needed.