Fixing Delegate's hash code's distribution (dotnet/coreclr#11019)

Fixing Delegate's hash code's distribution (dotnet/coreclr#11019)

Delegate's GetHashCode just returns the hash code of the delegate type. For a scenario where delegates are used as keys in a dictionary, this leads to obvious performance problems. We should look at coming up with a better GetHashCode that properly factors in the target object and method, in all of the various forms a delegate can take.

Commit migrated from https://github.com/dotnet/coreclr/commit/eb2d44e166f05e1d3da06925c39289bd2c4446a8