[TypeDefs] `Deno.core.heapStats()` Function Does Not Exist

[zicklag]

https://github.com/denoland/deno/blob/72199303d899b8ddf2ff46ed11bd513ed9cc47e2/core/lib.deno_core.d.ts#L71-L72

I might be missing something, but it appears that the heapStats() function documented here doesn't exist. I've attempted to run the function in a script with deno_core, but it wasn't found. Also, I can't seem to find an implementation of the operation in the Deno source.