column_condition is an LWT-specific boolean expression construct, but
recent work allowed it to be re-expressed in terms of generic expressions.
This series completes the work and eliminates the column_condition classes
and source file. Furthermore, a statement's IF clause is represented as a
single expression, rather than a vector of per-column conditions.
Closes#12597
* github.com:scylladb/scylladb:
cql3: modification_statement: unwrap unnecessary boolean_factors() call
cql3: modification_statement: use single expression for conditions
cql3: modification_statment: fix lwt null equality rules mangling
cql3: broadcast tables: tighten checks on conditions
cql3: grammar: communicate LWT IF conditions to AST as a simple expression
cql3: column_condition: fold into modification_statement
cql3: column_condition: inline column_condition_applies_to into its only caller
cql3: column_condition: inline column_condition_collect_marker_specification into its only caller
cql3: column_condition: eliminate column_condition class
cql3: column_condition: move expression massaging to prepare()
cql3: grammar: make columnCondition production return an expression
cql3: grammar: eliminate duplication in LWT IF clause "IN (...)" vs "IN ?"
cql3: grammar: remove duplication around columnCondition scalar/collection variants
cql3: grammar: extract column references into a new production
cql3: column_condition: eliminate column_condition::raw
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