[Spicy] Extend functionality of export in EVT files.

We now support selecting which fields of a unit type get exported into
the automatically created Zeek record; as well as selecting which
fields get a `&log` attribute added automatically to either all fields
or to selected fields.

Syntax:

- To export only selected fields:

    export Foo::X with { field1, field3 };

- To export all but selected fields:

    export Foo::X without { field2, field3 };

- To `&log` all fields:

    export Foo::X &log;

- To `&log` only selected fields:

    export Foo::X with { field1 &log, field3 }; # exports (only) field1 and field3, and marks field1 for logging

Syntax is still subject to change.

Closes #3218.
Closes #3219.

src/spicy/runtime-support.h

@@ -151,7 +151,7 @@ extern TypePtr create_enum_type(
     const std::string& ns, const std::string& id,
     const hilti::rt::Vector<std::tuple<std::string, hilti::rt::integer::safe<int64_t>>>& labels);
 
-using RecordField = std::tuple<std::string, TypePtr, hilti::rt::Bool>; // (ID, type, optional)
+using RecordField = std::tuple<std::string, TypePtr, hilti::rt::Bool, hilti::rt::Bool>; // (ID, type, optional, &log)
 extern TypePtr create_record_type(const std::string& ns, const std::string& id,
                                   const hilti::rt::Vector<RecordField>& fields);