Tracking issue for RFC 36: Async testbench functions

[zyp]

• RFC PR: Add an RFC for async testbench functions. rfcs#36
• Implementation PR: Implement RFC 36 #1344
• Documentation PR: Document the simulator #1374
• Removal of deprecation PR: N/A

[whitequark]

This still needs to be documented, so I'll keep it open for now.

[cr1901]

This still needs to be documented, so I'll keep it open for now.

Will generator functions be deprecated in 0.6 instead of 0.5? async testbenches made the 0.5 cutoff, and the RFC mentions deprecation of generator functions at the very end. But I don't see anything about deprecation in the CHANGELOG/porting guide from 0.4 to 0.5.

(Basically, "I'd like to quickly migrate to 0.5 and cut a release of some packages without upgrading generator testbenches to async for now.")

[whitequark]

Generator functions are deprecated in 0.5 and this is mentioned in the porting guide:

Convert simulator processes and testbenches to use the new async API.

However the deprecation fell through the cracks. (@wanda-phi do you think you can do another changelog backport PR?)