Allow translating non-constant NewExpression in translators and plugins

[roji]

We currently can't translate the following NodaTime expression:

var d = ctx.NodaTimeTypes.Single(t => t.LocalDate < new LocalDate(t.LocalDate.Year, 4, 21));

... since the constructor contains a non-evaluatable parameter. Ideally it should be possible to translate via a translator (like method or member), and exposed to plugins as well.

Low priority, at the moment am only aware of NodaTime types - but there may be others. Raised in npgsql/efcore.pg#1020.

Note that for DateTime this can be done in the SQL translating visitor, as it isn't a plugin.