looks nameof() is hard to change now, let's add a new one: stringof()

[Flithor]

As we know that nameof() always be requeired by some people to add some new behavior to make it can convert strings that contains more info.
But... how about a new one?
stringof()

it will convert the "strings" in it from orignal:

stringof(Level2Namespace.MyClass) //"Level2Namespace.MyClass"
stringof(RootNameSpace.Level2Namespace) //"RootNameSpace.Level2Namespace"
stringof(MyMethod(string, int)) //"MyMethod(string, int)"

Although it is indeed a bit longer than a normal string, but this "string" will support syntax nodes and IntelliSense.

[svick]

This is quite similar to #701.

[CyrusNajmabadi]

Moving to csharplang.