c-api: add wasi_config_set_stdin_bytes

[ShuP1]

As discussed in issue #4372 and respective issues about python and go bindings.

Can replace wasi_config_inherit_stdin in examples/wasi/main.c:78

wasi_config_t *wasi_config = wasi_config_new();
assert(wasi_config);
wasm_byte_vec_t binary;
wasm_name_new_from_string_nt(&binary, "sent to stdin");
wasi_config_set_stdin_bytes(wasi_config, &binary);
error = wasmtime_context_set_wasi(context, wasi_config);

(cc @alexcrichton)

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[alexcrichton]

Looks good to me, thanks for this! One small nit on the C side but otherwise I think this might also need a cargo fmt to pass CI.

[alexcrichton]

Since this takes owneship of the argument here I think it might be good to drop the const qualifier since it's actually mutated.

[alexcrichton]

Thanks again!