Corki needs better access to heal reduction

Corki doesnt have many options to deal with healing. Morello doesnt fit well into an AD build and armor pen stats are wasted on mortal reminder.

To address this issue I propose two options:

1. adding grievous wound effect to corki's E. this would allow him to burst some targets and have the damage stick during the combo while also not making him too oppressive in lane as the grievous is only active during his E trade window.
2. if option 1 doesnt work another idea would to give him some passive % armor pen to % magic pen conversion. this would not work on flat pen, so lethality builds would still do nothing, but it would open up build options such as mortal reminder, as some of that % pen would be utilized.