Add a crate to interface with the WebAssembly spec interpreter

The WebAssembly spec interpreter is written in OCaml and the new crate
uses `ocaml-interop` along with a small OCaml wrapper to interpret Wasm
modules in-process. The build process for this crate is currently
Linux-specific: it requires several OCaml packages (e.g. `apt install -y
ocaml-nox ocamlbuild`) as well as `make`, `cp`, and `ar`.

crates/fuzzing/wasm-spec-interpreter/tests/add.wat

@@ -0,0 +1,5 @@
+(module
+  (func (export "add") (param $a i32) (param $b i32) (result i32)
+    local.get $a
+    local.get $b
+    i32.add))

crates/fuzzing/wasm-spec-interpreter/tests/oob.wat

@@ -0,0 +1,5 @@
+(module
+  (memory (;0;) 0 0)
+  (func (export "oob")
+    i32.const 42
+    f32.load align=1))