re-add code tracking macroExpand times

[DSlug]

No description provided.

[danicheg]

I managed to validate this PR on the Scala-Steward repo. Several notes:

• expansionNanos became more plausible;
• expandedNodes are still blank for all entries.

From the perspective of practical benefits, it's better to have some intuitions about the time taken during macro expansions. I'm only concerned about examining why the original author pulled out of the library that approach for measuring. That was done intentionally, in one hop. But I also don't think I will manage to motivate myself to spend more time investigating this. Given that, I'll wait for a while until some miracle happens and someone either unconfuses this or I will merge PR one day and ship it as is.