Add optional Lit debug mode configuration option

[agjohnson]

Mostly just archiving this for later, I found this helpful in pinpointing what exactly was happening with Lit internals while working with FUI code that was conflicting:

window.emitLitDebugLogEvents = true;
window.addEventListener("lit-debug", (event) => {
  console.debug("Lit event:", event.detail);
});

In my case, when one of my LitElement properties was being updated, Lit was throwing an exception because the element changed outside control of Lit. I had to use debug output to figure out which property that was, and after that it was very easy to understand the conflict.

Be warned that this is a firehose of information though. I didn't want to add this under the existing debug flag because of how noisy it is.

[agjohnson]

cc @humitos as this may come in handy on Addons as well. This wasn't very well documented from Lit, I had to poke around to find this.

[humitos]

Be warned that this is a firehose of information though. I didn't want to add this under the existing debug flag because of how noisy it is.

In addons we have ?logging=debug that can be added to the URL for debug purposes. We can probably add this there: https://github.com/readthedocs/addons/blob/main/src/utils.js#L301-L313

[agjohnson]

I might suggest using a different parameter if so, logging=trace perhaps. The Lit debug logs every internal action and call through all of the web component lifecycle -- it is much more trace logging. It can be really noisy and would make other debug logs hard to use.