Use nodejs native abort-controller if available

[martinheidegger]

Node 15 added AbortController and AbortSignal to the global scope. This PR adds a ./node.js file that will use node.js globals if available and else falls back to the shim.

Note: I found it really hard to export AbortController as default AND add the AbortController/AbortSignal properties to it without extending AbortController so I dropped it. Sadly, this means that this PR is a breaking change as the default value is not available anymore.

Closes #24

[martinheidegger]

Node 16.3 has been released in the meantime.

[taras]

We see the same problem with Node 18 + TypeScript 4.9.

[pietrovismara]

Same here, @taras did you find any workaround?