Restructure find_path into a separate functions for modules and non-module items

Also renames `prefer_core` imports config to `prefer_no_std` and changes the behavior of no_std path searching by preferring `core` paths `over` alloc

crates/ide-diagnostics/src/handlers/missing_fields.rs

@@ -124,7 +124,7 @@ fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::MissingFields) -> Option<Vec<Ass
                         let type_path = current_module?.find_use_path(
                             ctx.sema.db,
                             item_for_path_search(ctx.sema.db, item_in_ns)?,
-                            ctx.config.prefer_core,
+                            ctx.config.prefer_no_std,
                         )?;
 
                         use_trivial_constructor(