Due to module loading parser has to do some not very appropriate for a parser things like

• expanding cfgs on modules (duplicated with expansion)
• keeping the current filesystem position (duplicated with expansion)

We also don't really need to load those files until we need to incorporate their contents into NodeId-entified AST, which happens during expansion.

The move will also mean never loading files in unconfigured code.
The loading is currently skipped only if cfg is placed directly on the mod m;, but not in other cases like

#[cfg(FALSE)]
mod m {
    mod n; // Still loaded
}