feat: add shim for fs

shims/fs.js

@@ -0,0 +1,56 @@
+const { FileSystem } = require('../src/index');
+
+let Provider;
+try {
+    Provider = require('fsprovider');
+}
+catch {
+    Provider = require('./providers/default');
+}
+
+const provider = new Provider();
+
+let onFsReady;
+let onFsError;
+
+let fsReady = new Promise((resolve, reject) => {
+  onFsReady = resolve;
+  onFsError = reject;
+});
+
+var fsInstance = new FileSystem({ provider }, (err) => {
+  if (err) {
+    onFsError(err);
+  } else {
+    onFsReady(true);
+  }
+});
+
+const fsPromises = new Proxy(fsInstance.promises, {
+  get(target, prop) {
+    return async (...args) => {
+      await fsReady;
+      return await target[prop](...args);
+    };
+  },
+});
+
+const fs = new Proxy(fsInstance, {
+  get(target, prop) {
+    if (prop === 'promises') {
+      return fsPromises;
+    }
+
+    return (...args) => {
+      (async () => {
+        await fsReady;
+        target[prop](...args);
+      })();
+    };
+  },
+});
+
+module.exports = {
+  __esModule: true,
+  default: fs,
+};