[IDE] Property delegate: Add custom attribute coloring test

Author: rintaro

test/IDE/coloring.swift

@@ -429,3 +429,13 @@ func foo() -> some P {}
 
 // CHECK: <kw>func</kw> foo() -> <kw>some</kw> <type>P</type> & <type>Q</type> {}
 func foo() -> some P & Q {}
+
+// CHECK: <kw>class</kw> PropertyDelgate {
+class PropertyDelgate {
+  // CHECK: @<type>MyDelegate</type>(<int>1</int>, receiveClosure {
+  @MyDelegate(1, receiveClosure {
+    // CHECK: <kw>var</kw> x = <int>1</int>; x
+    var x = 1; x
+  })
+  var something
+}