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-4.wat

@@ -0,0 +1,13 @@
+(module
+  (func (export "multiIf2") (param i32 i64 i64) (result i64 i64)
+    (local.get 2)
+    (local.get 1)
+    (local.get 0)
+    (if (param i64 i64) (result i64 i64)
+      (then
+        i64.add
+        i64.const 1)
+      ;; Hits the code path for an `else` after a block that does not end unreachable.
+      (else
+        i64.sub
+        i64.const 2))))