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-15.wat

@@ -0,0 +1,22 @@
+(module
+  (func (export "large-sig")
+    (param i32 i64 f32 f32 i32 f64 f32 i32 i32 i32 f32 f64 f64 f64 i32 i32 f32)
+    (result f64 f32 i32 i32 i32 i64 f32 i32 i32 f32 f64 f64 i32 f32 i32 f64)
+    (local.get 5)
+    (local.get 2)
+    (local.get 0)
+    (local.get 8)
+    (local.get 7)
+    (local.get 1)
+    (local.get 3)
+    (local.get 9)
+    (local.get 4)
+    (local.get 6)
+    (local.get 13)
+    (local.get 11)
+    (local.get 15)
+    (local.get 16)
+    (local.get 14)
+    (local.get 12)
+  )
+)