[Sol->Yul] Implementing getters for bytes and structs containing bytes member.

Co-authored-by: chriseth <chris@ethereum.org>

test/libsolidity/semanticTests/getters/bytes.sol

@@ -0,0 +1,10 @@
+contract C {
+    bytes public b;
+    constructor() {
+        b = "abc";
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// b() -> 0x20, 0x03, 0x6162630000000000000000000000000000000000000000000000000000000000