Add abstract method completion test (closes #3256)

tests/misc/projects/Issue3256/Main.hx

@@ -0,0 +1,10 @@
+abstract A(Int) from Int {
+    public function addFloat(f:Float):Float return this + f;
+}
+
+class Main {
+    static function main() {
+        var a:A = 1;
+        a.addFloat(
+    }
+}

tests/misc/projects/Issue3256/compile.hxml

@@ -0,0 +1 @@
+--display Main.hx@173

tests/misc/projects/Issue3256/compile.hxml.stderr

@@ -0,0 +1,4 @@
+<type>
+f : Float -&gt; Float
+</type>
+