Some missing tests

I'll list some stuff I come across which isn't covered by our unit tests:

* [x] self access on abstracts over abstracts (see https://github.com/haxetink/tink_core/blob/master/src/tink/core/Ref.hx)
* [x] unops on properties (see https://github.com/HaxeFoundation/haxelib/blob/development/src/haxelib/client/Main.hx#L1568)
* [x] omitted property accessor on externs (see https://github.com/HaxeFoundation/haxe/blob/development/std/cpp/VirtualArray.hx#L28)
* [x] `@:access` via base class (see nadako)
* [x] unops on abstract resolve (see https://github.com/HaxeFoundation/hxcpp/blob/master/tools/hxcpp/BuildTool.hx#L861)