Fix Encore.copyFiles() when copying images/fonts

[Lyrkan]

This PR fixes an issue that prevented Encore.copyFiles() from working properly when copying files that matched one of the default asset/resource rules.

Note that it has two drawbacks:

• it introduces what could be considered as a small breaking change for users calling configureLoaderRule('images', ...) or configureLoaderRule('fonts', ...) since it adds a new oneOf at the top-level of each rule
• if an user create a new rule that also matches files handled by Encore.copyFiles(...) they'll have to use the same oneOf/resourceQuery pattern to avoid conflicts

Closes #894

[weaverryan]

Thank you for checking into this complex bug @Lyrkan!