Generate internal dispatch only for functions that might actually get called via pointers

- This also adds support for internal library calls as a side-effect since they'll now be pulled into the internal dispatch automatically.

test/libsolidity/semanticTests/constructor/functions_called_by_constructor_through_dispatch.sol

@@ -0,0 +1,31 @@
+contract Test {
+    bytes6 name;
+
+    constructor() public {
+        function (bytes6 _name) internal setter = setName;
+        setter("abcdef");
+
+        applyShift(leftByteShift, 3);
+    }
+
+    function getName() public returns (bytes6 ret) {
+        return name;
+    }
+
+    function setName(bytes6 _name) private {
+        name = _name;
+    }
+
+    function leftByteShift(bytes6 _value, uint _shift) public returns (bytes6) {
+        return _value << _shift * 8;
+    }
+
+    function applyShift(function (bytes6 _value, uint _shift) internal returns (bytes6) _shiftOperator, uint _bytes) internal {
+        name = _shiftOperator(name, _bytes);
+    }
+}
+
+// ====
+// compileViaYul: also
+// ----
+// getName() -> "def\x00\x00\x00"