Fix edge cases with States.Array

[Fryguy]

• Array with 0 parameters
• Array with a single null parameter
• Array with a single Array parameter

@agrare Please review.

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To understand this better it's important to understand how parslet deals with maybe values. So, after fixing the simple args list to be a maybe (to allow 0 parameters), we'd end up with:

$ bin/console
irb(main):001:0> Floe::Workflow::IntrinsicFunction::Parser.new.parse("States.Array()")
=> {:states_array=>"States.Array()"@0}
irb(main):002:0> Floe::Workflow::IntrinsicFunction::Parser.new.parse("States.Array(1)")
=> {:states_array=>{:number=>"1"@13}}
irb(main):003:0> Floe::Workflow::IntrinsicFunction::Parser.new.parse("States.Array(1, 2)")
=> {:states_array=>[{:number=>"1"@13}, {:number=>"2"@16}]}

In other words, if you don't have any args, it returns the parsed slice (weird). With 1 arg it returns the arg directly, and with >1 arg, it returns them as an Array. So, to make this less complicated to transform, this PR introduces the args as a dedicated token.

The next problem you hit is as it resolves the args from the bottom up, you can end up with cases which conflict with existing transforms. For example,

• States.Array() will produce a tree like
  • {:states_array=>{:args=>nil}}
• States.Array(null) will produce a tree like
  • {:states_array=>{:args=>{:null_literal=>"null"@13}}}, and when that null_literal is processed from the bottom up, you'll get an intermediate tree of
  • {:states_array=>{:args=>nil}}

So, to solve this, we ensure that each arg is explicitly defined as an :arg in the parser. Thus the case above becomes:

• States.Array() will produce a tree like
  • {:states_array=>{:args=>nil}}
• States.Array(null) will produce a tree like
  • {:states_array=>{:args=>{:arg=>{:null_literal=>"null"@13}}}} and when that null_literal is processed from the bottom up, you'll get an intermediate tree of
  • {:states_array=>{:args=>{:arg=>nil}}}