async/await: direct transpilation to .then(...)?

[d180cf]

It's good that the current implementation can handle arbitrarily complex async functions, even with await statements inserted in arithmetic expressions run in a loop, but in most practical cases async functions can be easily transpiled into a chain of .then(...) calls. I'm wondering why this approach wasn't taken: transpiling to .then(...) if possible and transpiling to yield if not.

If would be nice to switch to async/await in my project, which is full of .then(...) chains, but it's not possible because even simplest async functions would turn into huge state machines that are neither readable nor debuggable.

[aluanhaddad]

Duplicate of #11725