Add combined_json_with_userdoc to command line tests

Author: wechman

test/cmdlineTests/combined_json_with_userdoc/args

@@ -0,0 +1 @@
+--combined-json userdoc --pretty-json --allow-paths .

test/cmdlineTests/combined_json_with_userdoc/c.sol

@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0
+pragma solidity >=0.0;
+
+contract C {}

test/cmdlineTests/combined_json_with_userdoc/input.sol

@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0
+pragma solidity >=0.0;
+
+import "./c.sol";

test/cmdlineTests/combined_json_with_userdoc/output

@@ -0,0 +1,15 @@
+{
+  "contracts":
+  {
+    "combined_json_with_userdoc/c.sol:C":
+    {
+      "userdoc":
+      {
+        "kind": "user",
+        "methods": {},
+        "version": 1
+      }
+    }
+  },
+  "version": "<VERSION REMOVED>"
+}