Make virtual delegate targets less costly (#87308)

Make virtual delegate targets less costly (#87308)

Saves 1.5% on the Stage2 app.

We make sure delegate targets are reflection visible to support Delegate.GetMethodInfo. When I originally did this work in #70198 I made a shortcut to avoid yet another node kind in the system (with a giant comment explaining what the problem is). But there's a lot of benefit in having this new node for apps with many reflection visible virtual methods.