Fix gnarly bug in Node and SpaceInsideBraces

[charlespwd]

Fixes #420

This fixes a LOT of bugs actually! This bug was like finding a little crack in a wall and then finding you have termites.

1. This is Liquid's raw output for the following tag:

   {%
     render
     'file'
   %}
   # expected
   => "render\n  'file'\n"
   # actual
   => "render 'file'\n"
   

   As you can see, not only do we not have the whitespace all the way till "render", we also don't have the whitespace between render and 'file'. This breaks all Position calculations since the needle does not exist in the source.

2. The implementation of whitespace_trimmed? didn't account for tags starting in the middle of a line. Or for tags starting on a different line

   <ul class="{%- if true -%}oh no{% endif %}">
   => not whitespace trimmed!
   {%-
     render 'oh no'
   -%}
   => not whitespace trimmed!
   

3. The implementation of whitespace_trimmed? assumed that it was trimmed in pairs (start and end) when it's possible to do it independently.

   {% assign true -%}
   => not whitespace trimmed!
   

4. Similarly a lot of our logic for space before/after tokens was wrong inside SpaceInsideBraces

5. Our implementation of inside_liquid_tag? was flipped. The tests were wrong and the implementation was too!

[macournoyer]

Wow amazing! Thanks for putting in the work to make this part solid 🙏

Just a couple questions and suggestions.

[macournoyer]

Can't be a variable & tag at the same time:

Suggested change

	output += "{{" if variable?
	output += "{%" if tag?
	if variable?
	output += "{{"
	elsif tag?
	output += "{%"
	end

Same bellow.

[macournoyer]

Do you have a sense if this is fixable in Liquid, or is just the way it works?

[charlespwd]

I think it would be fixable but the way tags are created you don't really know. We'd need to somehow pass it in the parse_context since we lose the information on tag creation (the tag_name and markup come in as two separate variables)

https://github.com/Shopify/liquid/blob/eab13a07d9861a38d993d2749ae25f06ff76426b/lib/liquid/tag.rb#L25-L37

[macournoyer]

Whoops! Actually found a tiny bug, checking Dawn:

▶ dev check ../dawn
Checking ../dawn ...
sections/image-banner.liquid:13: style: SpaceInsideBraces: Space missing before '%}'.
	<div id="Banner-{{ section.id }}" class="banner{% if section.settings.stack_images_on_mobile and section.settings.ima...
	                                                                          ^```

The `^` is not at the right place.

[charlespwd]

So the location is wrong, but the error is correct!

{% if section.settings.stack_images_on_mobile and section.settings.image != blank and section.settings.image_2 != blank%}

There's a missing space here!