[WIP] - 8.4 Asymmetric Visibility support

[genintho]

#1144

[genintho]

@czosel @cseufert This is work in progress, but I would like to hear your thoughts on the approach.

I tried to create a new token for protected(set) and private(set) but gave up after a bit as I could not find a good spot to do this.

I ended creating an intermediate object to store the various flags as it made things simpler to understand and removes a lot of duplication.

One thing I keep going back and forth is if the AST we create should match 100% the code or if it should match the intent of the code. For example public private(set) is the same as private(set). So do we want the AST to be same in both situation or not?