These allow linking multiple AbortControllers and ceate a timeout abort signal.

For example in case you want to abort a fetch in case

(1) the UI element gets removed
(2) a newer request replacing this one gets started
(3) a timeout happens because the fetch takes too long

createLinkedAbortController() allows merging multiple signals into one
and createTimeoutAbortSignal() allows creating a singal that auto aborts
after some time passes.

This generalizes the features of the events module and should replace it in the long run.

It allows simple pub/sub and retained events without a centralized instance.

While this will never work with old Edge it makes things easier during testing
where we can't set an id on the script tag. And we still don't know if supporting
old Edge is even needed.

This splits things into two phases, initAssetBaseURL() will try to set
a module wide base url for all assets.

The first code to use it successfully will define the asset base url for
all future getAssetURL() calls.

So that rollup can do tree shaking and report import errors.