Proposal to add a predefined type enumeration to IfcDocumentInformation

Currently there are three very similar attributes on IfcDocumentInformation:

- Purpose
- Intended Use
- Scope

These are [ambiguous](https://forums.buildingsmart.org/t/difference-between-purpose-intendeduse-and-scope-at-ifcdocumentinformation/895/2).

For the purposes of facility management, providing a standardised list of document types is desirable. Here is a list of proposed types from @billeast :

- Certificate
- Drawing - Design
- Drawing - Construction
- Drawing - Fabrication
- Drawing - Manufacturer
- Contractual
- Manufacturer Field Report
- Manufacturer Instruction
- Operation and Maintenance
- Submittal
- Photograph
- Product Data
- Report - Design
- Report - Product Test
- Report - System Test
- Specification
- Userdefined
- Notyetdefined

Start by reviewing IfcDocumentInformation and its Purpose, Intended Use, and Scope attributes in the IFC4.x specification. Compare the proposed document-type values with the existing schema conventions and determine how the predefined enumeration should relate to those attributes. Done means the enumeration design is agreed and the corresponding specification change is documented.

Written by the indexing model from the issue text.