Inspector proxy: Fix "Buffer() is deprecated" warning (facebook#43686)

Summary:

Under Node 20, the use of `new Buffer(string)` is deprecated and logs a warning. This replaces it with the recommended `Buffer.from(string)`.

Changelog: 
[General][Fixed] FIx "Buffer() is deprecated" warning from debugger proxy.

Reviewed By: huntie

Differential Revision: D55472025

packages/dev-middleware/src/inspector-proxy/Device.js

@@ -631,7 +631,7 @@ export default class Device {
             // $FlowFixMe[cannot-write]
             payload.params.sourceMapURL =
               'data:application/json;charset=utf-8;base64,' +
-              new Buffer(sourceMap).toString('base64');
+              Buffer.from(sourceMap).toString('base64');
           } catch (exception) {
             this.#sendErrorToDebugger(
               `Failed to fetch source map ${params.sourceMapURL}: ${exception.message}`,