Fix decorators overrides

[unflxw]

Use return value from hooks

The return value from decorators and overrides is ignored. Instead
of the returned span, the initial span (which may have been modified
in-place by the decorators or override) is used.

Delete the compose function, which is now unused.

Add span getters

Add getter methods for the span's properties, so users can inspect
the state of the span in overrides and make decisions based on it,
without having to dig into the undocumented ._data property.

Ignore errors after overrides

Run the logic to ignore an error based on its message and the
ignoreErrors configuration option after overrides have ran. This
allows overrides to be used to tweak the message to trigger or skip
the behaviour of this configuration option.

Allow ignoring spans in overrides

Allow for a span to be ignored by an override returning false from
it. Along with the getters, this allows customers to implement their
own span ignoring logic.

[backlog-helper]

✔️ All good!

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[tombruijn]

Please have a look at the broken build on CI and don't forget to add a changeset.

I'm also okay with making a breaking change as long as the version bump matches.

[tombruijn]

Can you add some unit tests for these new helpers?

[unflxw]

@tombruijn I took a look at the mismatches between types, and got so frustrated at the structure of the packages that I folded the core and types packages into the main javascript package.

In my view, this change removes a significant source of typing, packaging and distribution headaches, and was worth doing at some point. Let me know if you disagree, and also let me know if you think it deserves a greater version bump, or if marking types and core as deprecated on npm does suffice.

[tombruijn]

@unflxw I'm all for simplifying this integration. If we have less packages, go for it. From what I understand other packages do rely on these core and types packages, but also needed the appsignal/javascript package to function anyway.

Let me know when the build is green and I can review it :)