Clean up op registration

[bartlomieju]

Currently all registered ops are "added" as JavaScript bindings twice:

1. To Deno.core.ops module in: https://github.com/denoland/deno_core/blob/ce620969c447d5cd7d7c21e1b95bc120c67142be/core/runtime/bindings.rs#L268-L298

2. To ext:core/ops synthetic module in: https://github.com/denoland/deno_core/blob/ce620969c447d5cd7d7c21e1b95bc120c67142be/core/runtime/bindings.rs#L773-L796

We actually need both approaches - the former is for 01_core.js (that is a plain script and can't import ext:core/ops) and the latter for embedder code (though we still haven't migrated yet).

I think we could unify this - when getting exports for synthetic module we should assign ops to Deno.core.ops.

Alternative approach is that "internal ops" - ie. ops from deno_core could be added to Deno.core.ops and the remaining ops could be added to the synthetic module. Not sure yet, but I'll figure this out along the way.