Drop-in replacement for WeakMap that can store primitives.
const m = new HybridWeakMap([['foo', 42], ]);
Normally WeakMaps cannot store primitive values like Strings
or Numbers; this is mostly an implementation detail and there
still are some use cases where one would wish to store primitives
in a weak map even though those primitive values won't be garbage
This is what HybridWeakMap is for: It simply contains two maps; one
Weak map for objects, and one normal Map for primitives...