Remove single-use undeclared composer/pcre dependency with native preg_match

[jdworschak]

The single use of Composer\Pcre\Preg::isMatch in AbstractApi::parseLinkHeader relied on composer/pcre being available transitively via composer/xdebug-handler (a dev dependency of friendsofphp/php-cs-fixer). Downstream projects that install private-packagist/api-client without that chain hit a Class "Composer\Pcre\Preg" not found fatal at runtime when paginating any list endpoint.

This switches the one call site to native preg_match and removes the use import.
Trade-off vs. declaring composer/pcre as a runtime require is that Preg::isMatch throws on PCRE errors while preg_match(...) === 1 returns false on those errors and silently skips the if-block. For this simple regex against a server-generated Link header I personally feel the dependency is unwarranted.

[stevenrombauts]

Thanks!