Include argument labels in identifiers

[DevAndArtist (Adrian Meister)]

Here is a related thread I created two years ago:

Extending declaration names for closures

SE-0111 was accepted with a small temporary regression of loosing parameter labels in closures. In an extra commentary to this regression the core team pitched a solution that would be purely additive to the language without being a burden for the type system like pre SE-0111. The solution has to come in two steps: We have to extend the declaration names to allow labels in parentheses for variables, properties and parameters. (The following code snippet does not use , in between labels becau…