Add API for mapper plugins to directly alter Config Translation Form

Problem/Motivation

This is a follow-up to #2546212 Entity view/form mode formatter/widget settings have no translation UI 🐛 Entity view/form mode formatter/widget settings have no translation UI Needs review
Currently, the Config Translation module requires both a form alter and mapper classes separately to alter the configuration translation forms.
This issue proposes adding a new API to the mapper classes that would allow them to directly alter the config translation form. By providing this API, the need for separate form alter hooks and mapper classes will be eliminated, streamlining the process and making it more intuitive for developers.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet