Feature: Add support for spread operator

[zackad]

Close GH-44.

Partially depends on GH-16.

Need help on how to parse this expression

Error: Error: ERROR: Invalid map key
  32 | <twig:Component {{ ...vars }} />
  33 | {% set numbers = [1, 2, ...moreNumbers] %}
> 34 | {% set ratings = {'foo': 10, 'bar': 5, ...moreRatings} %}
     |                                        ^
  35 | 

[zackad]

Example of spread operator usage from twig documentation.

{% set numbers = [1, 2, ...moreNumbers] %}
{% set ratings = {'q1': 10, 'q2': 5, ...moreRatings} %}

{{ 'Hello %s %s!'|format(...['Fabien', 'Potencier']) }}

Ref: https://twig.symfony.com/doc/3.x/templates.html

[rellafella]

LGTM
I have just left the comment there about the precedence of the spread operator. My understanding is that as long as the precedence score is lower than that of the range operator .. (25), it should be fine.