Clear Shader Cache#708

If possible, add a clear cache or clear shader cache or both in the slippi options. Might cut down on serial laggers

also, have the ability to have it do it every time you start slippi, for the skin changing people out there.

this is already a part of the Soft Reset option in the launcher and is done automatically on dolphin updates. running every time you launch slippi is excessive and making that an option is not of interest when we only support vanilla