ENH: Default PredefinedType if not being set up

### Enhancement Description

Currently if elements have not set up any predefined types it export them to some "randomly selected" predefined types eg.:
Walls - STANDARD
Slab - FLOOR
Doors - DOOR
....

It would be more appropriate to set all non defined Predefined types to a constant value of "NOTDEFINED".

1. It will automatically inform receiver that these has not been properly classified

2. It will be constant in each IFC classes exported, as not every class has "STANDARD" predefined type, but every class have "NOTDEFINED" and "USERDEFINED" predefined type.

3. It will not cause misalignments with updating IFC Schema.for example IfcWall.STANDARD is deprecated from version 4.0 and should no longer be used.

### Revit Version

2026.0.x

### IFC for Revit Addon Version

26.1.0

### Windows Version

11 24H2

Start by locating the IFC export logic that assigns predefined types when an element has none; the issue does not name a file or test. Trace how different IFC classes select their defaults, then verify that unset types consistently export as NOTDEFINED and remain valid across the referenced IFC schema versions.

Written by the indexing model from the issue text.