[FLEDGE] Drop custom rudimentary console implementation.

Instead, use V8's builtin, and its use of Runtime.ConsoleAPIAdded that
devtools frontend already watches for.

To make this work reliably, associate the devtools agent pipe (and all
pipes that were already associated with it) with the worklet pipe.

Doing that directly would make DevToolsRendererChannel switch to preferring main channel to IO one, which wouldn't work with how our main channel event handling works. So, this also changes away from RendererChannel, since, well, we're not in a renderer in the first place.

Change-Id: Id1f7110f4f9305cc43a5a7dc125593c32f76a0d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3133443
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Maks Orlovich <morlovich@chromium.org>
Cr-Commit-Position: refs/heads/main@{#967440}