Remove dependency on wasmi

This is a pretty heavyweight dependency which accounts for a surprising amount
of runtime for larger modules in `wasm-bindgen`. We don't need 90% of the crate
and so this commit bundles a small interpreter for instructions we know are only
going to appear in describe-related functions.

crates/cli-support/src/descriptor.rs

@@ -94,7 +94,7 @@ pub enum VectorKind {
 impl Descriptor {
     pub fn decode(mut data: &[u32]) -> Descriptor {
         let descriptor = Descriptor::_decode(&mut data);
-        assert!(data.is_empty());
+        assert!(data.is_empty(), "remaining data {:?}", data);
         descriptor
     }