Merge pull request #6662 from ethereum/msgSender

Implement most trivial members.

test/libsolidity/semanticTests/viaYul/msg_sender.sol

@@ -0,0 +1,11 @@
+contract C {
+    function test() public view returns (bool) {
+        address x;
+        assembly { x := caller() }
+        return x == msg.sender;
+    }
+}
+// ====
+// compileViaYul: true
+// ----
+// test() -> true