Support Symfony 7

[tacman]

Currently composer.json only allows up to Symfony 6, but Symfony 7 will be out in less than 2 months.

This may be released to #173 , since asset() and importmap() have changes need to be reviewed here.

Symfony 4.4 will become unsupported next month, if it makes it easier to fix issues, I'd suggest dropping 4.4 and PHP < 8.1.