Extend using-for.

test/libsolidity/semanticTests/using/imported_functions.sol

@@ -0,0 +1,19 @@
+==== Source: A ====
+function inc(uint x) pure returns (uint) {
+    return x + 1;
+}
+
+==== Source: B ====
+contract C {
+	function f(uint x) public returns (uint) {
+        return x.f() + x.inc();
+    }
+}
+using {A.inc, f} for uint;
+import {inc as f} from "A";
+import "A" as A;
+// ====
+// compileViaYul: also
+// ----
+// f(uint256): 5 -> 12
+// f(uint256): 10 -> 0x16