Allow blocking for realtime

[daichifukui]

Hi,

I'd like to resolve #4738 with the two commits involved in this PR.

I'd be happy if you could review this and merge it if the changes are satisfactory.

Thanks.

[john-sharratt]

@daichifukui you can use these methods to enable blocking sleeps (its off by default now)

let mut ctx = WasiFunctionEnv::new();
ctx.data_mut().capabilities.threading.enable_blocking_sleep = true;

or

WasiEnvBuilder::capabilities/capabilities_mut

[daichifukui]

Thanks for merging this.
With the upstream Wasmer merged with this PR, the experimental result looks fine as expected.

$ cargo run --example wasi-manual-setup --release --features "cranelift,wasi,tokio,backend,wasi"
   Compiling wasmer-workspace v4.3.1 (/home/daichi/proj/00_research/wasmer)
    Finished release [optimized] target(s) in 10.09s
     Running `target/release/examples/wasi-manual-setup`
Compiling module...
Starting `tokio` runtime...
Creating `WasiEnv`...
Instantiating module with WASI imports...
Attach WASI memory...
Call WASI `_start` function...
Time elapsed is: 1.000473704s
Time elapsed is: 1.000321374s
Time elapsed is: 1.000355565s
Time elapsed is: 1.000525461s
Time elapsed is: 1.000523367s
Time elapsed is: 1.000522247s
Time elapsed is: 1.000340287s
Time elapsed is: 1.000248193s
Time elapsed is: 1.000456189s
Time elapsed is: 1.000468035s