Enable perfetto in workerd v8 build

[jasnell]

Patches v8's bazel build to allow building v8 with perfetto enabled.

Also, add perfetto traces for per-isolate boostrap.

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[fhanau]

That looks cleaner than I thought!

Two suggestions:

• We should disable perfetto in release builds based on the code size overhead using the flag we already have, and maybe make it off-by-default too. Turning it back on is as simple as adding --//src/workerd/util:use_perfetto=True
• You may want to use v8_flag() for the perfetto define in the patch, that way it should be easy to upstream. Keeping perfetto configurable would be kinda tricky, but you could define a bazel config that sets the existing use_perfetto setting and the V8 flag at once.

[jasnell]

... We should disable perfetto in release builds

since we're already building with perfetto enabled (and using it in prod) enabling this in v8 adds at most roughly 0.227% to the file size. If we want, we want disable for opt/release builds but that's something we can easily do as a separate PR I think.

[jasnell]

use v8_flag() for the perfetto define

@fhanau ... not sure what you mean.

[fhanau]

use v8_flag() for the perfetto define

@fhanau ... not sure what you mean.

v8_flag() is a macro used in V8's BUILD.bazel to configure V8 defines and make them easy to turn on/off. If we want to upstream this patch, that's probably the right approach to use for consistency with other defines. An LLM should be able to do it if you feed it my prior comment.
It's not exactly blocking though so I stamped the PR, I just think that doing it that way could make this patch easy for us to upstream. For our purposes the patch is clean enough so it can go ahead as-is if you want to

[npaun]

Reviewed this cause I like to keep up with our build changes