Move symfony/console, var-dumper and var-exporter to the 6.4 LTS line #596

Summary

Move symfony/console, symfony/var-dumper and symfony/var-exporter from the 5.4 line to the 6.4 LTS line. Part of the PHP 8.1 update (#595).

Why

composer.json requires ^5.4 for all three. Symfony 6.4 needs PHP 8.1, which #595 makes the minimum, so the 6.4 LTS line is now installable. After composer update on PHP 8.1, the other Symfony components in the dependency tree (event-dispatcher, filesystem, finder, process, yaml and others) are already on 6.4, while these three stay on 5.4 only because of our constraints.

Current state

• symfony/console is used in 11 files under src (CliCommand extends Symfony's Command, plus the console boot stages and commands).
• symfony/var-exporter is used in 3 files.
• symfony/var-dumper is required but not imported anywhere in src or the tests. It may be there for the global dump() and dd() functions that applications call.

Proposed change

• composer.json: ^6.4 for the three packages.
• Fix what Symfony 6 requires: return types on the Command methods that CliCommand and the commands override, and anything else the test suite or PHPStan reports.
• Check whether symfony/var-dumper is still needed, and say so in the changelog if it is removed.
• Check that php qt list and a few commands still work in the starter project.

Out of scope

• Symfony 7 (needs PHP 8.2).
• Changing the commands' public behavior.

Breaking changes

• Possibly the signatures of CliCommand methods, if Symfony's new return types reach the commands applications write. To be confirmed during the work.

Acceptance criteria

• the three packages are on 6.4
• composer test, composer cs:check, composer phpstan and composer rector:check pass
• php qt works in the starter project
• the changelog describes any signature change

Notes

Relevant code: composer.json, src/Console, src/App/Adapters/Console.