Consider using normal random instead of crypto random for IDs

[anuraaga]

Currently, cryptographic randoms are used for IDs I think.

https://github.com/open-telemetry/opentelemetry-go/blob/master/sdk/trace/trace.go#L18

This generally has a far larger impact on the CPU usage of a user's app than normal random (I've seen 10% of CPU used on ID generation before when using crypto random). You can see some benchmarks and discussion for JS here

open-telemetry/opentelemetry-js#1334

It'd probably be good to use normal random here too, like in JS, Java, Python (when I filed the JS issue, I misread the Go code thinking it was already using normal random ;) ).

/cc @wilguo

[Aneurysm9]

I'm not sure this change is useful. We're currently only using the crypto/rand package for obtaining seed data for a PRNG from the math/rand package. ID generation is performed with a PRNG from the math/rand package already.

[anuraaga]

Ah got it, didn't realize the crand is only for the seed. Looks good then.