Error if there are pending items on the event queue

[jeffcharles]

We've received feedback that the current behaviour of successfully exiting when items there are items enqueued on to the event loop that will never be executed is unexpected and they would prefer if the execution trapped with a helpful error message instead. This PR:

• Adds an is_pending to Context to return whether there are pending jobs on the event queue
• Changes the run bytecode logic to panic if there are pending jobs on the event queue with an exception if we're running the Web Platform Tests suite as the suite enqueues a promise as part of its setup
• Disables a WPT suite that enqueues events

The check if we're running the WPT suite is done through a WASI environment variable. I opted to use this approach because:

• I couldn't figure out a reasonable way to change how we run the WPT suite so that it doesn't enqueue the promise
• we won't have to use a special build of Javy for the WPT suite
• we don't have to touch the Javy CLI including adding support for additional arguments or env vars and plumbing it through to the core logic

I did take a look at the benchmarks to see if the WASI call to retrieve the env var value would have a performance impact and the results indicated no change in performance between main and this branch.

[jianghong]

For when we release: Would you consider this a major change?

[jianghong]

It's unclear to me why this was needed to be commented out, could you clarify?

[jeffcharles]

This actually doesn't need to be commented out any more since I disabled the error message with pending jobs. Technically the tests aren't completing properly but I can't figure out a way to have these tests error but have the suite setup to not cause a panic.

[jeffcharles]

So this does need to continue to be commented out or we get unhandled promise rejections due to Javy not implementing XMLHttpRequest when we run with the event loop enabled. I've updated the comment.

[jianghong]

I don't know much about how the wpt stuff is built and ran yet but could we run it with the experimental_event_loop feature turned on? Would that help avoid needing to pass and checking this JAVY_WPT?

[jeffcharles]

Tried to address that in #277 (comment). The short answer is yes, but I'd prefer to not do that because WPT would be testing something that doesn't behave like Javy would without the feature enabled.

[jeffcharles]

For when we release: Would you consider this a major change?

We can bump the minor version since we're 0.x. JS code that was working could stop working if it created pending jobs.

[saulecabrera]

LGTM; thanks for all your patience iterating on this!