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-8.wat

@@ -0,0 +1,12 @@
+(module
+  (func (export "f") (param i64 i32) (result i64)
+    (local.get 0)
+    (local.get 1)
+    ;; If with else. Same number of params and results.
+    (if (param i64) (result i64)
+      (then
+        (drop)
+        (i64.const -1))
+      (else
+        (drop)
+        (i64.const -2)))))