test that first argument of extension method is stripped for completion (closes #3261)

tests/misc/projects/Issue3261/Main.hx

@@ -0,0 +1,11 @@
+using Main.A;
+
+class A {
+    public static function f(v:String, b:Int):String return v;
+}
+
+class Main {
+    static function main() {
+        "a".f(
+    }
+}

tests/misc/projects/Issue3261/compile.hxml

@@ -0,0 +1 @@
+--display Main.hx@147

tests/misc/projects/Issue3261/compile.hxml.stderr

@@ -0,0 +1,4 @@
+<type>
+b : Int -&gt; String
+</type>
+