[LiquidDoc] Support param type validations when value is a variable

[jamesmengo]

I feel like it can be done. Not sure if there is a clean way but want to capture it in a ticket.

E.g. If you visit the AssignMarkup, you can see what type it is under node.value.expression.type. But i do this this fails pretty quickly for complex assigns:

{% assign foo = product.handle | filter1 | filter 2 %}

We have a symbols table in TypeSystem (packages/theme-language-server-common), but we'd have to move it over. We can investigate this after though.

Originally posted by @aswamy in #792 (comment)