Use ? for Mapping Result Errors

[smores56]

To promote Roc developers providing context for Results when propagating errors with try, we want to add a new operator ? that acts as a Result.mapErr equivalent. Some example usages:

fileContents =
    try File.read! "file.txt" ? FailedToReadFile

fileContents =
    try File.read! "file.txt"
        ? FailedToReadFile

{} = File.save! "file.txt" contents ? \err =>
    Logging.error! "Failed to save file.txt: $(Inspect.toStr err)"

    FailedToSaveFile err

It should be higher precedence than try such that try will propagate errors after ? is applied, but it does not need to be used with try.

We should always attempt to format onto the same line as the fallible code, but can optionally wrap to a newline with an indentation to imply continuation; this prevents code from reading like we apply ? after try.

The new ? operator should be able to handle mapping over errors using pure or effectful mappers, meaning it should be its own AST node. We can start with a pure-only implementation, since we are waiting on purity inference still.

If a pure handler is used with the new ?? "Result.withDefault" operator, we should raise a warning that the error mapping is unnecessary, since it will always be discarded by ??.