cql3: expr: detemplate find_in_expression
cql3: expr: detemplate find_in_expression

find_in_expression() is not in a fast path but is quite large
and inlined due to being a template. Detemplate it into a
recurse_until() utility function, and keep only the minimal
code in a template.

The recurse_until is still inline to simplify review, but
will be deinlined in the next patch.

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla