cranelift: move wasmtests in cranelift-wasm

Move test data used by cranelift-wasm's tests in
the crate directory, to make the tests autonomous.

Fixes #2910

cranelift/wasm/wasmtests/multi-16.wat

@@ -0,0 +1,9 @@
+(module
+  (func (export "param") (param i32) (result i32)
+    (i32.const 1)
+    (if (param i32) (result i32) (local.get 0)
+      (then (i32.const 2) (i32.add))
+      (else (i32.const -2) (i32.add))
+    )
+  )
+)