[v8] Refactor usages of `span.startChild()` to `startInactiveSpan()`

[mydea]

We have some leftover usages of span.startChild(). Some of them are related to #10898, but others are standalone and should be refactored to just create a span based on the active span.

In most cases, we can probably refactor them to just use startInactiveSpan instead, unless we need the span to be active (which is rarely the case, as far as I could see).

I would ignore the usage in old node for now, we can remove this eventually.

### Tasks
- [ ] https://github.com/getsentry/sentry-javascript/pull/10956
- [ ] https://github.com/getsentry/sentry-javascript/pull/10943
- [x] MAYBE: Refactor `startChild` usage in node & node performance integrations - probably safe to ignore this for now