Compatibility shim does not allow 2 args or an empty window caption

[DanRathbun]

@thomthom : But features/behaviour in UI.inputbox that was useful and not buggy can of course be adopted here.

Yes, the native UI.inputbox has the ability to pass 1 prompt array argument without a window title.
But it stupidly will not allow 2 args with the 2nd being the window title. (It raises an exception.)

Your code mimicked this. So I reordered the statements in the ArgumentParser to allow anywhere from 1..4 args.
A consumer can now do ...

HtmlUI::inpubox(["Name"], "Who are you?")

It is silly to force coders to stuff empty literal arrays into a method call, ie ...

HtmlUI::inpubox(["Name"], [], "Who are you?")

If there are no defaults, there is no good reason to force the passing of an empty array.
(This is forced inclusion of empty array arguments is a native UI::inputbox quirk.)

---

In testing this I also found that the argument parser sets the window :title to an empty string to mimic the native UI::inputbox which will display without a window caption. (Ie, the compatibility shim method does not allow the default Sketchup::app_name to be the default window caption.)

But this doesn't work with a Chromium window. If the window title is not set or is an empty string, then the window caption gets set to "inputbox.html".

The solution is to insert a space into an empty :title string if it is left empty (ie, not specified in the compatibility shim arguments.)

[DanRathbun]

Just FTR ... the following is the get_options_args method reordered with much annotations added.
I simplified the code a bit as I thought using the arguments hash just complicated the reading of the code.

In this version I stripped out the support for class identifier defaults and the whitespace pad warnings, so as not to confuse this issue. The snippet below is meant to show the annotations I added and how the :title handling code was reorderd a bit to allow for 1 arg with a blank window title and 2 args where the second arg is a title string.

    def get_options_args(*args)
      unless args.size.between?(1,4)
        fail(ArgumentError,'No arguments given. (1..4 expected)',@callstack)
      end

      # Begin with default arguments:
      title    = ''
      prompts  = ensure_array(args, 0)
      defaults = []
      lists    = []

      # Extract the arguments from the args array:

      # The position of the `:title` argument depends upon whether the
      # method was called with `defaults` or `list` array arguments.
      # Start with minimum position 2 (at index 1):
      title_index = 1

      # The defaults to match the prompts:
      if args.size > 1 && args[1].is_a?(Array)
        defaults = ensure_array(args, 1)
        # NOTE: At this point the first 2 args are known arrays.
        # The defaults array can be larger as extras will be ignored.
        # The defaults also can be empty, ie no defaults given.
        # Any shortage of defaults will get nil assigned.

        title_index += 1
      end

      # The lists of options:
      if args.size > 2 && args[2].is_a?(Array)
        # NOTE: Empty string options map to empty arrays:
        lists = args[2].map { |list| list.to_s.split('|') }

        title_index += 1
      end

      # Get the window title if given:
      if args.size > title_index
        title = args[title_index].to_s
      end

      # Convert to window property hash:
      options = {
        inputs: []
      }

      # Title finalization:
      # Empty `:title` results in "inputbox.html" as the window caption.
      # So for a blank window caption there must be at least 1 space.
      options[:title] = title.empty? ? ' ' : title

      # For each prompt, build an input control property hash:
      prompts.each_with_index { |prompt, index|
        # Init this input property hash:
        input = {
          # Label
          label: prompt.to_s,
          value: '',
          options: [],
          type: 'textbox'
        }
        # Default and Value:
        default = defaults[index]
        if default.nil?
          input[:default] = ''
        else
          input[:value]= input[:default]= default
        end
        # Options
        list = lists[index]
        if list && !list.empty?
          input[:type] = 'dropdown'
          # Check if we should leave render control as unchosen:
          if input[:default] != '' && !input[:value].empty? && !list.include?(default)
            input[:value] = ''
          end
          input[:options] = list
        end
        # Push the input property hash into the inputs array:
        options[:inputs] << input
      }
      options
    end

---

I also added the signature 4 places in the docs.

YARD has a way of doing this one place and the referencing it in other docstrings.
But I don't know who would run YARD on such a small code repo.

    #
    # @overload inputbox(prompts, title = '')
    #   The signature uses all textbox inputs without defaults.
    #   @param [Array<String>] prompts
    #   @param [String] title