Liquid::C parses liquid filter arguments with dashes in them, Liquid does not.
For tags that accept kwargs and dumps them on the HTML tag, this is an important feature.
e.g. {{ ... | image_tag: loading: 'lazy', data-something: 'value!' }}
Without this change, Liquid would incorrectly parse the
`data-something` kwarg as a single argument and would skip over the
invalid characters.
See https://github.com/Shopify/theme-check/issues/539 for more context
This fixes theme-check#218, wherein variables used in echo tags are not
considered used by the linter. It is because our visitor doesn't see the
:variable_lookup's in the echo tag since the children array is empty.
But this array is empty because it is swallowed by the @variable.