Add support for conditional extras

We don't support the conditional at the moment for concatenated scripts.

Conditionally loaded scripts should be excluded from concatenation.

Related core code: https://core.trac.wordpress.org/browser/trunk/src/wp-includes/class.wp-scripts.php#L269

Start with the linked WordPress class.wp-scripts.php entry point around line 269, then inspect this plugin's concatenation path to see how conditional scripts are handled. Done means conditionally loaded scripts are excluded from concatenated resources; the issue mentions no test file, so identify the relevant existing test or verification path first.

Written by the indexing model from the issue text.