core: rename heapStats to memoryUsage

[AaronO]

This PR aligns the name and output fields with node, since that's "standard" and there's nothing wrong with it.

The arrayBuffers field is 0, since we don't track ArrayBuffer allocation individually, but could with a custom allocator, but I think that's a separate issue.

Partially fixes #9980

Sample output

❯ ./target/debug/deno eval "console.log(Deno.core.memoryUsage())"
{ rss: 3363056, heapTotal: 4243456, heapUsed: 3561772, external: 0, arrayBuffers: 0 }

Questions

1. Should we expose this directly on Deno and move it to stable ?

[ry]

Why not just Deno.memoryUsage() ?

[AaronO]

Why not just Deno.memoryUsage() ?

Will do, if we're ok landing this as stable. Will add types and re-export it as Deno.memoryUsage() similar to how we re-export Deno.core.close()

[AaronO]

@ry I've removed the arrayBuffers field and re-exported it as Deno.memoryUsage(), so this should be good to merge.

[bartlomieju]

LGTM