It's very annoying to add a declaration to expression.hh and watch
the whole world get recompiled. Improve that by moving less-common
functions to a new header expr-utils.hh. Move the evaluation machinery
to a new header evaluate.hh. The remaining definitions in expression.hh
should not change as often, and thus cause less frequent recompiles.
Closes#14346
* github.com:scylladb/scylladb:
cql3: expr: break up expression.hh header
cql3: expr: restrictions.hh: protect against double inclusions
cql3: constants: deinline
cql3: statement_restrictions: deinline
cql3: deinline operation::fill_prepare_context()
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