This PR introduces improvements to `expr::to_restriction` and prepares the validation part for restriction classes removal.
`expr::to_restriction` is currently used to take a restriction from the WHERE clause, prepare it, perform some validation checks and finally convert it to an instance of the restriction class.
Soon we will get rid of the restriction class.
In preparation for that `expr::to_restriction` is split into two independent parts:
* The part that prepares and validates a binary_operator
* The part that converts a binary_operator to restriction
Thanks to this split getting rid of restriction class will be painless, we will just stop using the second part.
`to_restriction.cc` is replaced by `restrictions.hh/cc`. In the future we can put all the restriction expressions code there to avoid clutter in `expression.hh/cc`.
This change made it much easier to fix#10631, so I did that as well.
Fixes: #10631Closes#10979
* github.com:scylladb/scylla:
cql-pytest: Test that IS NOT only accepts NULL
cql-pytest: Enable testInvalidCollectionNonEQRelation
cql3: Move single element IN restrictions handling
cql3: Check for disallowed operators early
cql3: Simplify adding restrictions
cql3: Reorganize to_restriction code
cql3: Fix IS NOT NULL check in to_restriction
cql3: Swap order of arguments in error message