vfs: remove duplicated module resolution logic from setup.js

Remove ~550 lines of duplicated module resolution functions that
reimplemented canonical Node.js resolver behavior (extension trying,
package exports resolution, bare specifier walking, directory entry
resolution, format detection). The canonical resolvers already consult
VFS through the loader overrides installed by installModuleLoaderOverrides(),
making the Module.registerHooks() resolve/load hooks redundant.

Also add clearStatCache() to the CJS loader, called on VFS unmount to
prevent stale stat cache entries from causing incorrect resolution after
a VFS is deregistered.

Author: mcollina

lib/internal/modules/cjs/loader.js

@@ -113,6 +113,7 @@ const kFormat = Symbol('kFormat');
 
 // Set first due to cycle with ESM loader functions.
 module.exports = {
+  clearStatCache,
   kModuleSource,
   kModuleExport,
   kModuleExportNames,
@@ -229,6 +230,16 @@ let requireDepth = 0;
 let isPreloading = false;
 let statCache = null;
 
+/**
+ * Clear the stat cache. Called when VFS instances are unmounted
+ * to prevent stale stat results from being returned.
+ */
+function clearStatCache() {
+  if (statCache !== null) {
+    statCache = new SafeMap();
+  }
+}
+
 /**
  * Internal method to add tracing capabilities for Module._load.
  *