Proposal: Better support for Out Parameters by introducing Out Variables

C# got Out Variables in 7.0 - [Mads wrote about here](https://blogs.msdn.microsoft.com/dotnet/2017/03/09/new-features-in-c-7-0/).

Out Variables would extend the usage of "As Type" ([see here](https://github.com/dotnet/vblang/issues/59)) by an additional scenario in VB. When using Out Parameters, we would not need to declare the Out Parameter Variable beforehand, but could use it like this:

```
Dim intAsString = "314159"

'An Out Variable would be declared and passed to the method in one go.
Dim boolResult = Integer.TryParse(intAsString, intResult As Integer)

'And it would be used it in the same scope.
intResult = intresult * 2
```