Rewrite interpreter generically (#2323)

* Rewrite interpreter generically

This change re-implements the Cranelift interpreter to use generic values; this makes it possible to do abstract interpretation of Cranelift instructions. In doing so, the interpretation state is extracted from the `Interpreter` structure and is accessed via a `State` trait; this makes it possible to not only more clearly observe the interpreter's state but also to interpret using a dummy state (e.g. `ImmutableRegisterState`). This addition made it possible to implement more of the Cranelift instructions (~70%, ignoring the x86-specific instructions).

* Replace macros with closures

cranelift/filetests/src/function_runner.rs

@@ -237,6 +237,7 @@ impl UnboxedValues {
             DataValue::F32(f) => ptr::write(p as *mut Ieee32, *f),
             DataValue::F64(f) => ptr::write(p as *mut Ieee64, *f),
             DataValue::V128(b) => ptr::write(p as *mut [u8; 16], *b),
+            _ => unimplemented!(),
         }
     }