2.x: Remove checked exceptions from transformer interfaces?

[JakeWharton]

Now that transformers are not Function extensions, does it makes sense that they allow throwing checked exceptions? When a transformer is being invoked, its job is taking an observable and transforming it into another observable but not actually doing any real work. Thus, it seems strange that you would ever encounter something that threw a checked exception in this operation. It would be a sign that you need to move that work into the stream pipeline instead of the observable creation pipeline.

This also makes code that has to deal with transformers annoying because they now have to handle (aka wrap and throw) these checked exceptions.

Happy to send a PR, but wanted to get some thoughts first and make sure I wasn't missing anything.

[akarnokd]

Works for me both ways so its up to the community to decide.

[JakeWharton]

Ok. Sent a PR for it. No rush to merge if you want to wait for other opinions.

[dlew]

I'm a fan of this change, for the reason stated above - due to its nature, a transformer should rarely (never?) be throwing a checked exception.

[akarnokd]

I thought about it and couldn't find a reason to allow throwing there.

Closing via #4710.