Fix a race condition in classic edit toolbar setup

Fix a race condition in classic edit toolbar setup

mediawiki.action.edit used to call mw.toolbar.init on its own during DOMReady -- this required that the module already be loaded *before* DOMReady, *and* that it be fully loaded before the immedate-execution code that sets up the default toolbar items (output from EditPage.php).
This failed since we've gone fully async in the bottom-loading items, and could result in failed calls to mw.toolbar.addButton.

Wrapped those immediate calls in a mediawiki.loader.using call to ensure they're run after the module is loaded, and moved the mw.toolbar.init call into that section so we guarantee it gets run first.