Work around issues with Deno 1.31+

[evanw]

Version 0.20.0 of esbuild changed how the esbuild child process is run in esbuild's API for Deno. Previously it used Deno.run but that API is being removed in favor of Deno.Command. As part of this change, esbuild is now calling the new unref function on esbuild's long-lived child process, which is supposed to allow Deno to exit when your code has finished running even though the child process is still around (previously you had to explicitly call esbuild's stop() function to terminate the child process for Deno to be able to exit).

However, this introduced a problem for Deno's testing API which now fails some tests that use esbuild with error: Promise resolution is still pending but the event loop has already resolved. It's unclear to me why this is happening. The call to unref was recommended by someone on the Deno core team, and calling Node's equivalent unref API has been working fine for esbuild in Node for a long time. It could be that I'm using it incorrectly, or that there's some reference counting and/or garbage collection bug in Deno's internals, or that Deno's unref just works differently than Node's unref. In any case, it's not good for Deno tests that use esbuild to be failing.

In this PR, I am removing the call to unref to fix this issue. This means that you will now have to call esbuild's stop() function to allow Deno to exit, just like you did before esbuild version 0.20.0 when this regression was introduced.

Note: This regression wasn't caught earlier because Deno doesn't seem to fail tests that have outstanding setTimeout calls, which esbuild's test harness was using to enforce a maximum test runtime. Adding a setTimeout was allowing esbuild's Deno tests to succeed. So this regression doesn't necessarily apply to all people using tests in Deno.

Fixes #3682