vscode API - network proxy support: basic auth

[alexr00]

 3) vscode API - network proxy support
       basic auth:
     Error: Unexpected status code (expected 418): 200
      at ClientRequest.<anonymous> (extensions/vscode-api-tests/src/singlefolder-tests/proxy.test.ts:115:14)
      at Object.onceWrapper (node:events:634:26)
      at ClientRequest.emit (node:events:531:35)
      at HTTPParser.parserOnIncomingClient (node:_http_client:698:27)
      at HTTPParser.parserOnHeadersComplete (node:_http_common:119:17)
      at TLSSocket.socketOnData (node:_http_client:540:22)
      at TLSSocket.emit (node:events:519:28)
      at addChunk (node:internal/streams/readable:559:12)
      at readableAddChunkPushByteMode (node:internal/streams/readable:510:3)
      at TLSSocket.Readable.push (node:internal/streams/readable:390:5)
      at TLSWrap.onStreamRead (node:internal/stream_base_commons:191:23)

https://dev.azure.com/monacotools/Monaco/_build/results?buildId=287247&view=logs&j=9833cdaa-2e92-5f8d-56a8-239fd18fd628&t=e6d1c856-dd40-5946-2df0-58cb7c21b113&s=a56e7651-4213-56af-9488-c25fe636c10c

[bhavyaus]

Seeing recent failures: https://dev.azure.com/monacotools/Monaco/_build/results?buildId=313007&view=results

[chrmarti]

Improved the test in #237890. 🤞

[bhavyaus]

Failing in recent builds: https://github.com/microsoft/vscode/pull/237964 https://github.com/microsoft/vscode/pull/237971