Type annotation for patterns

[martin-ilgner]

Tries to resolve the issues mentioned in #1308

[phischu]

Great! Please add a test file examples/pos/pattern_annotations.effekt with the examples from the linked issue.

[martin-ilgner]

Done. But there is a problem:

str match {
  case "hello" => "world"
  case s: String => s
  case _ => "bye"
}

is wrongly parsed. It takes the match arrow as part of a function type. But still fails with Expected => but got keyword case

[martin-ilgner]

Should I also try to understand the Typer and use the parsed TypeAnnotation?

Edit: Too complicated