Add Keystone Affix: Shielding

Add Keystone Affix: Shielding is sold by the Keystone Vendor for .
It adds the Shielding affix to a Mythic Keystone. However, the affix never made it out of the patch 10.1.0 PTR so this item may likely not be offered in future tests.
==Patch changes==
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==External links==