Move metro-inspector-proxy into dev-middleware

Summary:
X-link: facebook/react-native#39045

## Context

RFC: Decoupling Flipper from React Native core: react-native-community/discussions-and-proposals#641

## Changes

- Relocates `metro-inspector-proxy` source from the Metro repo into the React Native repo as part of the `react-native/dev-middleware` package.
    - Drops the `runInspectorProxy` entry point.
- Attaches the Inspector Proxy to the `createDevMiddleware()` API as the new integration point for this functionality.
- Documents migrated endpoints + usage of `createDevMiddleware()` in README.

Changelog: [Internal]
Metro changelog: None (`metro-inspector-proxy` is now an internal component of `react-native`, covered in the [release notes for 0.78.1](https://github.com/facebook/metro/releases/tag/v0.78.1))

Reviewed By: motiz88, blakef

Differential Revision: D48066213

fbshipit-source-id: 3fbef5d881f6f451cb5955dcbbc362c53347437e

flow-typed/npm/debug_v2.x.x.js

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ * @format
+ */
+
+// https://github.com/visionmedia/debug
+// https://www.npmjs.com/package/debug
+
+declare module 'debug' {
+  declare module.exports: (namespace: string) => (...Array<mixed>) => void;
+}