runtime: document explicitly that finalizers and cleanups can hold up other finalizers and cleanups

[mknyszek]

We should add a sentence to the finalizer and cleanup documentation that makes it abundantly clear a finalizer/cleanup can hold up other ones. We should also list this as one of the complications of using them in https://go.dev/doc/gc-guide.

[gabyhelp]

Related Issues

• runtime: finalizers/cleanups can exit the finalizer goroutine #71824
• runtime: SetFinalizer documentation ambiguous or confusing #24480 (closed)
• runtime: add debug mode for finalizers and cleanups #72949

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