Make async-io optional for people who only want to use the executor.

[najamelan]

Currently, async-io is marked as an optional dependency in Cargo.toml, but when not on wasm, it's always turned on on async-global-executor. Would it be possible to make it truly optional for people who only want to use the executor?

[AMythicDev]

I too would like to see this as in my current project I want to use the task::spawn function without pulling other dependencies.

A way could be to put the task module or it's related functions on a gated feature (similar to how tokio does it) and include it in the default feature, so that no downstream code breaks.