`--check-php-configuration` CLI option for checking whether PHP is configured for testing

[sebastianbergmann]

Motivated by #6294, I would like to have the following:

❯ ./phpunit --check-php-configuration
PHPUnit 12.4-geb984b78f8 by Sebastian Bergmann and contributors.

Checking whether PHP is configured according to https://docs.phpunit.de/en/12.4/installation.html#configuring-php-for-development

display_errors = On             ... ok
display_startup_errors = On     ... ok
error_reporting = -1            ... ok
xdebug.show_exception_trace = 0 ... ok
zend.assertions = 1             ... ok
assert.exception = 1            ... ok
memory_limit = -1               ... ok

[sebastianbergmann]

Once this feature is released the issue template should be updated to require the output of --check-php-configuration for bug reports.