node: unbundle simdutf

[carlocab]

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We unbundled merve in 90df578. merve
depends on simdutf, and we don't want to load two different versions
of simdutf in-process. This means we should try to unbundle simdutf
too.

[cho-m]

The sub-directory part will need some extra logic to allow skipping a directory, maybe via nil input.

Also, there is another simdutf that cannot be unbundled included in V8.

• Extend shared simdutf flag to v8 nodejs/node#60984

I think default build would use the copy in V8 in all locations (V8, node and merve).

• https://github.com/nodejs/node/blob/v25.9.0/deps/merve/merve.gyp#L11-L17
• https://github.com/nodejs/node/blob/v25.9.0/deps/v8/third_party/simdutf/BUILD.gn

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It would be simpler to disable simdutf in merve but there is a performance cost.

Though, we haven't enabled simdutf in ada-url while it is enabled upstream so whatever we do should match for merve and ada-url:

• https://github.com/nodejs/node/blob/v25.9.0/deps/ada/ada.gyp#L11-L17

[GunniBusch]

The sub-directory part will need some extra logic to allow skipping a directory, maybe via nil input.

Also, there is another simdutf that cannot be unbundled included in V8.

• Extend shared simdutf flag to v8 nodejs/node#60984

I think default build would use the copy in V8 in all locations (V8, node and merve).

• https://github.com/nodejs/node/blob/v25.9.0/deps/merve/merve.gyp#L11-L17
• https://github.com/nodejs/node/blob/v25.9.0/deps/v8/third_party/simdutf/BUILD.gn

It would be simpler to disable simdutf in merve but there is a performance cost.

Though, we haven't enabled simdutf in ada-url while it is enabled upstream so whatever we do should match for merve and ada-url:

• https://github.com/nodejs/node/blob/v25.9.0/deps/ada/ada.gyp#L11-L17

also i think there is already a pr that proposed a shared v8, corresponding to the issue nodejs/node#53509, but was closed because the branch was deleted.
nodejs/node#62097

But I am currently experimenting with these changes and try to maybe open another pr upstream and here to add support for devendoring v8. (I think they want proof that it works hence a pr here)