Consider using separate form for filtering translations

Problem/Motivation

In 📌 Refactor translation UI/form Active , I had to add a custom controller to be able to return the necessary AJAX responses of the pager links. The form seems to be okay, but logically it covers two separate functionality:

1. Filtering the results
2. Manipulating translations (create / update / delete), changing status of the source string.

Imho, it would be a good idea to separate this two functionality also at the code level.

Proposed resolution (high level)

1. Create a separate form class for the filter form, keep it as a "get" form
2. Improve the controller of the pager's route so that it can replace the route what the translate form's route provides. E.g. Use form builder to first build the filter form, then build the pager, and then, also add the actual translate form (with the table) to the route's renderable array

Remaining tasks

TBD

User interface changes

Nothing.

API changes

Nothing.

Data model changes

Nothing.