Add `random_get()` to the ABI

[mandarjog]

A high quality random number is needed for many reasons inside a Wasm module.

wasi_ephemeral_random.get defines such an API. proxy_wasm should use or define a compatible API.

[mandarjog]

@PiotrSikora

[mathetake]

@mandarjog it's now supported in cpp-host proxy-wasm/proxy-wasm-cpp-host#68, and it's upstreamed to Envoy's master branch envoyproxy/envoy#13606

[sonhal]

How can this be called from Rust? Cannot find a mention of it in the Rust SDK

[PiotrSikora]

How can this be called from Rust? Cannot find a mention of it in the Rust SDK

See the answer in the other issue you've opened in the Rust SDK.