Fix the fixme on r88053: dependency handling was broken in debug mode in certain...

Fix the fixme on r88053: dependency handling was broken in debug mode in certain cases. More specifically, if A is a file module that depends on B, B is a wiki module that depends on C and C is a file module, the loading order is CBA (correct) in production mode but was BCA (wrong) in debug mode. Fixed this by URL-ifying scripts and styles for those modules in debug mode, as I said to on CR. What this means is that the initial debug=true request for a module will now always return arrays of URLs, never the JS or CSS itself. This was already the case for file modules (which returned arrays of URLs to the raw files), but not for other modules (which returned the JS and CSS itself). So for non-file modules, load.php?modules=foo&debug=true now returns some JS that instructs the loader to fetch the module's JS from load.php?modules=foo&debug=true&only=scripts and the CSS from ...&only=styles .

* Removed the magic behavior where ResourceLoaderModule::getScripts() and getStyles() could return an array of URLs where the documentation said they should return a JS/CSS string. Because I didn't restructure the calling code too much, the old magical behavior should still work.
* Instead, move this behavior to getScriptURLsForDebug() and getStyleURLsForDebug(). The default implementation constructs a single URL for a load.php request for the module with debug=true&only=scripts (or styles). The URL building code duplicates some things from OutputPage::makeResourceLoaderLink(), I'll clean that up later. ResourceLoaderFileModule overrides this method to return URLs to the raw files, using code that I removed from getScripts()/getStyles()
* Add ResourceLoaderModule::supportsURLLoading(), which returns true by default but may return false to indicate that a module does not support loading via a URL. This is needed to respect $this->debugRaw in ResourceLoaderFileModule (set to true for jquery and mediawiki), and obviously for the startup module as well, because we get bootstrapping problems otherwise (can't call mw.loader.implement() when the code for mw.loader isn't loaded yet)