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/call-simd.wat

@@ -0,0 +1,14 @@
+(module
+  (func $main
+    (v128.const i32x4 1 2 3 4)
+    (v128.const i32x4 1 2 3 4)
+    (call $add)
+    drop
+  )
+  (func $add (param $a v128) (param $b v128) (result v128)
+    (local.get $a)
+    (local.get $b)
+    (i32x4.add)
+  )
+  (start $main)
+)