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esm: refactor hooks – add loader instances

Rodrigo Muino Tomonari requested to merge github/fork/izaakschroeder/esm-loader-instances into main

Previously we had one array for each kind of chain in the variable #chains; this is probably the most efficient, but it decouples the connection between the original register call and the hook functions themselves.

By adding #loaderInstances we can keep track of each time register is called. This allows, for example, trivially removing the loader later on, or associating shared context with a particular register call. The tradeoff here if we just did this would be that during hook traversal we may iterate over a slightly larger number of objects. Instead we keep #chains but it is now a derived property; every time #loaderInstances changes we simply rebuild #chains.

This sets the stage for doing other things, like adding deregister: https://github.com/nodejs/node/pull/49159 or adding the ability to attach local state to individual loader instances.

N.B. I should probably add back the documentation about the entries in #chains somehow.

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