Update loaderId description for requestWillBeSent and responseReceived network events

[2tunnels]

Updated the loaderId description in the Network.requestWillBeSent and Network.responseReceived events to mention that they might be empty for preflight requests, not just worker requests. Thought this would make things clearer for anyone digging into network request details.

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[Lightning00Blade]

The definition are coming from Chromium/DevTools repo and need to update there. For Chromium Repo - https://chromium.googlesource.com/chromium/src/+/main/docs/contributing.md And the file location is https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/public/devtools_protocol/browser_protocol.pdl