`v8::Isolate::AttachCppHeap` is deprecated

[targos]

See: https://github.com/nodejs/node-v8/actions/runs/6742272834/job/18328109270
Refs: v8/v8@d5631f6

This breaks us here: https://github.com/nodejs/node-v8/blob/1ccbbfef3a32dbce7d5f35f17c2280bc995af10e/src/env.cc#L552
And here: https://github.com/nodejs/node-v8/blob/1ccbbfef3a32dbce7d5f35f17c2280bc995af10e/src/env.cc#L583

/cc @nodejs/cpp-reviewers @dharesign

[targos]

test/cctest/test_cppgc.cc is also affected.

[targos]

Ping. This is soon going to be a problem.

[joyeecheung]

It seems to me that we can just skip the attach and detach call at all and V8 can handle it for us? (We previously already do "if there isn't one, create one, otherwise use the existing one" which seems to be what V8 does internally now) cc @mlippautz

[joyeecheung]

Or specifically is this branch always true now? Then we can just remove the else branch and the branch in IsolateData::~IsolateData

https://github.com/nodejs/node-v8/blob/1ccbbfef3a32dbce7d5f35f17c2280bc995af10e/src/env.cc#L524-L527

[targos]

It's entirely possible that this is easy to fix. I just am not able to do it myself with my knowledge of C++.

[joyeecheung]

I can check later to see if that branch is always true now. If it is we can delete the extra handling.

[targos]

I pushed a buildable version of the canary branch today.

[targos]

Moved to core repo as the code is now in main.

[targos]

Related: v8#209