Expand examples to show FinalizationRegistry usage for binding GC and deallocation

I am trying to port a c++ library to deno and I am not clear on how gc with ffi buffers works.

This is a great explanation of how ffi works, but I cannot understand the connection with gc.

I saw this example

https://github.com/aapoalas/denonomicon/blob/5da9957a350e146aec203b93bb8621805569f8c0/examples/cpp/inheritedClass.ts#L225C7-L225C26

but I do not understand how the gc is informed that it needs to call a destructor when the buffer/pointer goes out of scope in deno.

I have done the same in node and a function like this

https://nodejs.org/api/n-api.html#napi_create_external

makes it super easy.

I could not understand what is the equivalent in deno.