YulUtilFunctions: convertionFunction() to also handle array string/memory casts.

test/libsolidity/semanticTests/conversions/string_to_bytes.sol

@@ -0,0 +1,9 @@
+contract C {
+	function f(string memory s) public pure returns (bytes memory t) {
+		t = bytes(s);
+	}
+}
+// ====
+// compileViaYul: also
+// ----
+// f(string): 32, 5, "Hello" -> 32, 5, "Hello"