Named arguments for processes and workflows

[bentsherman]

Closes #2257 #3507

Adds a take option for process inputs that is similar to the emit option for outputs. Processes and workflows can now be invoked with named arguments, using the same syntax as native Groovy functions.

Additionally, you don't have to specify the take option in the input declaration if the process input has a simple name. For inputs with e.g. GStrings, closures, tuples, the take option must be explicit.

It works by interpreting the first process / workflow argument as the named arguments map if it is a map. We have to do this because the invocation happens through WorkflowBinding.invokeMethod() rather than an actual function definition. So there will be a problem if you call a process and the first argument is a map, but you meant for that argument to be for the first process input (i.e. as a value channel).

One way that we could avoid this problem is to refactor the NextflowDSL AST transformation to convert process and workflow definitions into actual function definitions, so that the process/workflow inputs are defined as native function arguments.

[bentsherman]

Gonna fold this one into #4553 doing something like this:

process foo {
  input:
    List<Path> inputs
    String args = ''
  output:
    stdout
  script:
    """
    foo_cmd ${args} ${inputs}
    """
}

workflow {
  // positional args
  foo( files('*.foo'), '--custom-option' )

  // named args
  foo( inputs: files('*.foo'), args: '--custom-option' )

  // mixing is not allowed
}