feature(dev-middleware): add custom message handlers to extend CDP capabilities (#43291)

Summary:
This is a proposal for the `react-native/dev-middleware` package, to allow implementers to extend the CDP capabilities of the `InspectorProxy`. It's unfortunately needed until we can move to the native Hermes CDP layer.

At Expo, we extend the CDP capabilities of this `InspectorProxy` by injecting functionality on the device level. This proposed API does the same, but without having to overwrite internal functions of both the `InspectorProxy` and `InspectorDevice`.

A good example of this is the network inspector's capabilities. This currently works through the inspection proxy, and roughly like:
- Handle any incoming `Expo(Network.receivedResponseBody)` from the _**device**_, store it, and stop event from propagating
- Handle the incoming `Network.getResponseBody` from the _**debugger**_, return the data, and stop event from propagating.

This API brings back that capability in a more structured way.

## API:

```ts
import { createDevMiddleware } from 'react-native/dev-middleware';

const { middleware, websocketEndpoints } = createDevMiddleware({
  unstable_customInspectorMessageHandler: ({ page, deviceInfo, debuggerInfo }) => {
    // Do not enable handler for page other than "SOMETHING", or for vscode debugging
    // Can also include `page.capabilities` to determine if handler is required
    if (page.title !== 'SOMETHING' || debuggerInfo.userAgent?.includes('vscode')) {
      return null;
    }

    return {
      handleDeviceMessage(message) {
        if (message.type === 'CDP_MESSAGE') {
          // Do something and stop message from propagating with return `true`
          return true;
        }
      },
      handleDebuggerMessage(message) {
        if (message.type === 'CDP_MESSAGE') {
          // Do something and stop message from propagating with return `true`
          return true;
        }
      },
    };
  },
});
```

## Changelog:

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[GENERAL] [ADDED] - Add inspector proxy device message middleware API

Pull Request resolved: https://github.com/facebook/react-native/pull/43291

Test Plan: See added tests and code above

Reviewed By: huntie

Differential Revision: D54804503

Pulled By: motiz88

fbshipit-source-id: ae918dcd5b7e76d3fb31db4c84717567ae60fa96

packages/dev-middleware/src/createDevMiddleware.js

@@ -9,6 +9,7 @@
  * @oncall react_native
  */
 
+import type {CreateCustomMessageHandlerFn} from './inspector-proxy/CustomMessageHandler';
 import type {BrowserLauncher} from './types/BrowserLauncher';
 import type {EventReporter} from './types/EventReporter';
 import type {Experiments, ExperimentsConfig} from './types/Experiments';
@@ -61,11 +62,12 @@ type Options = $ReadOnly<{
   unstable_experiments?: ExperimentsConfig,
 
   /**
-   * An interface for using a modified inspector proxy implementation.
+   * Create custom handler to add support for unsupported CDP events, or debuggers.
+   * This handler is instantiated per logical device and debugger pair.
    *
    * This is an unstable API with no semver guarantees.
    */
-  unstable_InspectorProxy?: Class<InspectorProxy>,
+  unstable_customInspectorMessageHandler?: CreateCustomMessageHandlerFn,
 }>;
 
 type DevMiddlewareAPI = $ReadOnly<{
@@ -80,16 +82,16 @@ export default function createDevMiddleware({
   unstable_browserLauncher = DefaultBrowserLauncher,
   unstable_eventReporter,
   unstable_experiments: experimentConfig = {},
-  unstable_InspectorProxy,
+  unstable_customInspectorMessageHandler,
 }: Options): DevMiddlewareAPI {
   const experiments = getExperiments(experimentConfig);
 
-  const InspectorProxyClass = unstable_InspectorProxy ?? InspectorProxy;
-  const inspectorProxy = new InspectorProxyClass(
+  const inspectorProxy = new InspectorProxy(
     projectRoot,
     serverBaseUrl,
     unstable_eventReporter,
     experiments,
+    unstable_customInspectorMessageHandler,
   );
 
   const middleware = connect()