Move to the try Keyword for Error Propagation

[smores56]

We are currently using the ? suffix operator to desugar to Result.try, which allows users to propagate errors early. We want to move to supporting the try prefix keyword, which can be used in values and in pipelines. Example usage looks like the following:

fileContent = try File.read! "file.txt"

jsonData =
    try File.read! "file.txt"
    |> try Json.decode 

try usages early return errors to the nearest function boundary, by basically desugaring to

when result is
    Err err -> return Err err
    Ok val ->
        # rest of the body using val

We need #7104 to be implemented first to implement try.

We should not treat try as a simple desugaring to Result.try, as it needs to eventually work with pure and effectful code. That's why we should desugar to a when statement instead.