ESQL: isNotNullAndFoldable should not perform a fold

[alex-spies]

This helper method is used in type checks/resolutions and checks whether a value is not null.

This check really shouldn't happen at the time when we perform type resolutions - type resolutions shouldn't depend on individual values.

More importantly, folding values can be expensive - we should only perform this in the ConstantFolding and FoldNulls steps of the logical optimizer.

We may be able to use the Validatable interface to perform the null-check after the logical optimizer step, when all foldables can be assumed to be already folded.

This is currently used in Top, FullTextFunction and Match.

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[alex-spies]

Additionally marking this as a bug because this is relevant to the memory tracking that is being added in #118602.