http2: allow passing FileHandle to respondWithFD

This seems to make sense if we want to promote the use
of `fs.promises`, although it’s not strictly necessary.

PR-URL: nodejs/node#29876
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

doc/api/http2.md

@@ -1450,7 +1450,7 @@ server.on('stream', (stream) => {
 <!-- YAML
 added: v8.4.0
 changes:
-  - version: v12.12.0
+  - version: REPLACEME
     pr-url: https://github.com/nodejs/node/pull/29876
     description: The `fd` option may now be a `FileHandle`.
   - version: v10.0.0

lib/internal/fs/promises.js

@@ -512,29 +512,33 @@ async function readFile(path, options) {
 }
 
 module.exports = {
-  access,
-  copyFile,
-  open,
-  opendir: promisify(opendir),
-  rename,
-  truncate,
-  rmdir,
-  mkdir,
-  readdir,
-  readlink,
-  symlink,
-  lstat,
-  stat,
-  link,
-  unlink,
-  chmod,
-  lchmod,
-  lchown,
-  chown,
-  utimes,
-  realpath,
-  mkdtemp,
-  writeFile,
-  appendFile,
-  readFile
+  exports: {
+    access,
+    copyFile,
+    open,
+    opendir: promisify(opendir),
+    rename,
+    truncate,
+    rmdir,
+    mkdir,
+    readdir,
+    readlink,
+    symlink,
+    lstat,
+    stat,
+    link,
+    unlink,
+    chmod,
+    lchmod,
+    lchown,
+    chown,
+    utimes,
+    realpath,
+    mkdtemp,
+    writeFile,
+    appendFile,
+    readFile,
+  },
+
+  FileHandle
 };

lib/internal/http2/core.js

@@ -91,11 +91,7 @@ const {
   },
   hideStackFrames
 } = require('internal/errors');
-const { validateNumber,
-        validateString,
-        validateUint32,
-        isUint32,
-} = require('internal/validators');
+const { validateNumber, validateString } = require('internal/validators');
 const fsPromisesInternal = require('internal/fs/promises');
 const { utcDate } = require('internal/http');
 const { onServerStream,