[Intelligent code completion] Support collection retrieved via its name

[Poitrin]

Created by
Shopify/theme-liquid-docs#18

Describe the bug
Intelligent Code Completion does not support collection retrieved via its name.
Therefore, collections.first.products is supported, but collections['sale-potions'].products isn't.

Expected
In the example …

{% for x in collections['sale-potions'].products %}
    {{- x.█

… x should be treated as a product, so that suggestions for product (available, collections, compare_at_price, …) are displayed at the cursor's position.

Actual

x seems to be treated as a collection, so that suggestions for collection are displayed.