`expression`'s default constructor is dangerous as an it can leak
into computations and generate surprising results. Fix that by
removing the default constructor.
This is made somewhat difficult by the parser generator's reliance
on default construction, and we need to expand our workaround
(`uninitialized<>`) capabilities to do so.
We also remove some incidental uses of default-constructed expressions.
Closes#14706
* github.com:scylladb/scylladb:
cql3: expr: make expression non-default-constructible
cql3: grammar: don't default-construct expressions
cql3: grammar: improve uninitialized<> flexibility
cql3: grammar: adjust uninitialized<> wrapper
test: expr_test: don't invoke expression's default constructor
cql3: statement_restrictions: explicitly initialize expressions in index match code
cql3: statement_restrictions: explicitly intitialize some expression fields
cql3: statement_restrictions: avoid expression's default constructor when classifying restrictions
cql3: expr: prepare_expression: avoid default-constructed expression
cql3: broadcast_tables: prepare new_value without relying on expression default constructor
ea9db1b35c