In various places of the codebase, function_exists calls are employed to allow usage of functions introduced in recent PHP versions without breaking backwards compatibility. This has two major downsides namely:

• having more complicated code at current, as two implementations need to be maintained
• these might be harder to spot and replace in the future, when a higher PHP version is enforced and thus these checks become obsolete.

Therefore this PR proposes to use the Symfony polyfills instead. This will ensure the functions are available on all supported PHP versions, thus retaining backwards compatibility, without requiring any code modifications. Moreover, given these are easily findable in the corresponding composer.json files, they can be easily removed in the future when the PHP version is raised, without further checking which functions correspond to which PHP version.