Attempt to properly implement ? and + signature semantics

[mikhail-barg]

This PR attempts to address #776

I'm referring to the docs on + and ? and my interpretation of these lines is as follows:

• if an argument with ? does not match anything, it gets no value => gets undefined;
• if an argument with + matches multiple values, it gets an arry of these values as a value (because there's no other way to pass multiple values into a single argument), so:
  • n+ matching 1.0 would result in a literal 1.0
  • n+ matching 1.0, 2.0, 3.0 woul result in array [1.0, 2.0, 3.0]

As you may see, I've only changed recently added 035 and 040 tests to match the semantics above, so I believe this change is not a major breaking change. It's more like covering previously vague topic. I've also added a number of tests to display the behaviour more explicitly.

@andrew-coleman what do you think?

[Turings98apprentice]

While I would agree that the docs do not seem to match the current behavior, I do believe this is a breaking change, because it changes how function arguments are set. JSONata scripts written before this change would have no guarantee of working the same after this change.

I think this is a step in the right direction for function signatures, but I also think we need to examine this issue a little deeper before making v3.0. For example, there are still other [undocumented (oops)] issues with how function signatures work that we should make an effort to address/correct in the same version jump (imo).