Support + and - for delegate combine and remove

[AnthonyDGreen]

Today in VB if you want to combine delegates or remove them you have to use shared methods on the delegate type, which are also loosely typed. We could support + and - like C# for combining two delegate invocation lists or removing a delegate from the invocation list of another. Option Strict users have requested this for a while.

Note: This proposal is for combining delegates not for using += and -= for event handler registration and removal. VB already has AddHandler and RemoveHandler for this.