feat: add fully_qualified_strict_types fixer import_relative_symbols option

[mvorisek]

finish after #7719

TODO for myself - import \Ns\Exception even if there is \Exception in the code before

[Wirone]

As I already mentioned, I would prefer import_symbols to be bool or ['classes' => true, 'constants' => true, 'functions' => true, 'allow_relative' => true] (all options related to importing grouped under main option), with normaliser defined to support both (bool value means all the sub-options takes that value). I even have it implemented locally, just did not have time to finish it 😅.

This is only early feedback after seeing PR, did not take a look at implementation yet.