Support for ? operator (Try trait)

[wcarmon]

Can we have support for the ? operator on LocalResult

I believe this means impl Try for LocalResult

https://doc.rust-lang.org/std/ops/trait.Try.html

[djc]

That's not stable yet, which means it would entail adding at least a Cargo feature to optionally enable this... I think it's pretty messy and there's not enough value in doing so until the trait stabilizes.

[wcarmon]

Reasonable.

[esheppa]

@wcarmon - you also probably don't want to use ? with LocalResult as you will generally want to handle all the possibilities or transform it to some other type. In future we will likely change the API to have some convenience methods to get a best effort local timestamp, see: #716