Prettier Liquid: VariableLookup in drops

[charlespwd]

Not expecting a lot of different formatting except for things like spaces inside lookups and nested lookups.

Things to support:

{{ variable }}
{{ variable.property }}
{{ variable.property-with-dashes }}
{{ variable["property with quotes"] }}
{{ variable[other_variable] }}
{{ [global] }}
{{ 1 }}
{{ true }}
{{ empty }}
{{ "string" }}
{{ 'string' }}
{{ (0..2) }}

This difference should be that we'll print those as lookups instead of passthrough markup. Just that should be a lot of refactoring and ohm syntax updates.