Add "in" operator as syntactic sugar for a chain of "or" expressions

In data analysis it is common to retrieve data that matches one of several distinct values, reflected in SQL as the IN operator.

This is syntactic sugar, so we need to balance between a convenient notation and adding value to the expression syntax that we already have.

1) Using JSON collections and a new "in" operator:

CountryCode in ["US","CA","DE"]

or in a more URL-friendly notation (as double quotes and square brackets require percent-ending)

CountryCode in ('US','CA','DE')

2) Allowing arbitrary collection expressions on the left side of lambda expressions:

["US","CA","DE"]/any(c:c eq CountryCode)

3) Adding an overload to the contains function:

contains(["US","CA","DE"], CountryCode)