Fix: move "user" attribute from field to type

The "user" field attribute (copy from userspace) is not taken into
account in the bytecode specialization and interpreter recursive
traversal through composed types (LOAD_FIELD bytecode instructions).

Those are currently used by the event notification capture bytecode, and
by filter expressions which access fields nested within composed types.

Move the "user" attribute from the event fields to the integer and
string types. This will allow ensuring that the bytecode specialization,
interpreter and event notification output capture have access to this
user attribute even in nested types (e.g. arrays, sequences) in a
subsequent change.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I044a0845b256b5e2cf65aa0888af2b906678d19d