[Forwardport] Add missing implementation for applySortOrder()

[rostyslav-hymon]

Original Pull Request

magento#13641

Description

The totals block for the frontend order view has a method applySortOrder to manipulate ordering of already added totals. Alas this method was never implemented.

It is also currently not used in the core, so this PR is only a partial solution to the issue linked below. But having it implemented is useful for third party extensions as a sensible way to reorder the totals.

Fixed Issues (if relevant)

1. Totals sort order is not respected in customer account order view magento/magento2#13631:Totals sort order is not respected in customer account order view (not fixed but related)

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)