Add support for the experimental wasi-crypto APIs (#2597)

* Add support for the experimental wasi-crypto APIs

The sole purpose of the implementation is to allow bindings and
application developers to test the proposed APIs.

Rust and AssemblyScript bindings are also available as examples.

Like `wasi-nn`, it is currently disabled by default, and requires
the `wasi-crypto` feature flag to be compiled in.

* Rename the wasi-crypto/spec submodule

* Add a path dependency into the submodule for wasi-crypto

* Tell the publish script to vendor wasi-crypto

crates/wasi-crypto/src/wiggle_interfaces/mod.rs

@@ -0,0 +1,38 @@
+use std::rc::Rc;
+
+use wasi_crypto::CryptoCtx;
+
+wiggle::from_witx!({
+    witx: ["$CARGO_MANIFEST_DIR/spec/witx/wasi_ephemeral_crypto.witx"],
+    ctx: WasiCryptoCtx
+});
+
+pub mod wasi_modules {
+    pub use super::{
+        wasi_ephemeral_crypto_asymmetric_common, wasi_ephemeral_crypto_common,
+        wasi_ephemeral_crypto_kx, wasi_ephemeral_crypto_signatures,
+        wasi_ephemeral_crypto_symmetric,
+    };
+}
+
+pub use types as guest_types;
+
+#[derive(Clone)]
+pub struct WasiCryptoCtx {
+    ctx: Rc<CryptoCtx>,
+}
+
+impl WasiCryptoCtx {
+    pub fn new() -> Self {
+        WasiCryptoCtx {
+            ctx: Rc::new(CryptoCtx::new()),
+        }
+    }
+}
+
+mod asymmetric_common;
+mod common;
+mod error;
+mod key_exchange;
+mod signatures;
+mod symmetric;