This adds initial, unstable, support for the wasm32-wasi target. Not all of Tokio's
features are supported yet as WASI's non-blocking APIs are still limited.
Refs: tokio-rs/tokio#4827
Functions that may panic can be annotated with `#[track_caller]` so that
in the event of a panic, the function where the user called the
panicking function is shown instead of the file and line within Tokio
source.
This change adds `#[track_caller]` to all the non-unstable public APIs
in tokio-stream (only `chunks_timeout` in `StreamExt`) where the
documentation describes how this function may panic due to incorrect
input.
A test has been included to cover the panic.
Refs: #4413
