Codegen for object access.

test/libyul/objectCompiler/dataoffset_self.yul

@@ -0,0 +1,16 @@
+object "a" {
+  code { sstore(0, dataoffset("a")) }
+  data "data1" "Hello, World!"
+}
+// ----
+// Assembly:
+//     /* "source":22:48   */
+//   0x00
+//     /* "source":29:30   */
+//   0x00
+//     /* "source":22:48   */
+//   sstore
+// stop
+// data_acaf3289d7b601cbd114fb36c4d29c85bbfd5e133f14cb355c3fd8d99367964f 48656c6c6f2c20576f726c6421
+// Bytecode: 6000600055fe
+// Opcodes: PUSH1 0x0 PUSH1 0x0 SSTORE INVALID