Incorrect error when specifying a Property value and omitting a dataType

See https://github.com/buildingSMART/IDS/issues/331#issuecomment-2225619660 and https://github.com/buildingSMART/IDS/issues/337

Seems there's been some back and forth over whether dataType is mandatory when specifying a property value. Currently validating an IDS such as

```xml

Test of conformity






IFCSPACE






Pset_SpaceOccupancyRequirements


OccupancyType


9.2

```

... will give a warning
```
info: idsTool.Program[0] Auditing: Ids structure, Ids content.
info: idsTool.Program[0] Auditing file: `.../space.ids`.
info: idsTool.Program[0] The file schema version is: Ids1_0
[**omitted other warnings in this file**]
fail: idsTool.Program[0] Error 203: Incompatible constraints on `property` element at line X, position Y, specifiying a 'value' requires a 'dataType'.
...
```

According to @CBenghi's comment in https://github.com/buildingSMART/IDS/issues/206#issuecomment-1923702315 it's now optional.