Improve AbortController polyfill to be more realistic

[sujayakar]

currently we have an AbortController stub (

convex-backend/npm-packages/udf-runtime/src/03_abort_signal.ts

Line 7 in 1478c1d

global.AbortController = AbortController;

) which doesn't work well. instead of throwing uncatchable developer errors, its properties are undefined. we can't change it to throw errors because that would break existing usage. but having undefined properties is unexpected and can cause subtler errors and bugs.

see deno's implementation for inspiration: https://github.com/denoland/node_test/blob/1c9511e584eb9d465bcd4b1e6c05ecedf7f15549/test/parallel/test-abortcontroller.js#L39
https://github.com/denoland/deno/blob/28834a89bb85d708ec7b67ab844724e1221cc6cf/ext/web/03_abort_signal.js#L290
https://github.com/denoland/deno/blob/28834a89bb85d708ec7b67ab844724e1221cc6cf/ext/web/03_abort_signal.js#L4

we'll want to have web spec compliance tests in isolate/tests