Moving some struct tests to semanticTests

test/libsolidity/semanticTests/abiEncoderV2/struct/mediocre_struct.sol

@@ -0,0 +1,14 @@
+pragma experimental ABIEncoderV2;
+
+contract C {
+    struct S { C c; }
+    function f(uint a, S[2] memory s1, uint b) public returns (uint r1, C r2, uint r3) {
+        r1 = a;
+        r2 = s1[0].c;
+        r3 = b;
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// f(uint256,(address)[2],uint256): 7, 0, 0, 8 -> 7, 0, 8