Use of AdministrableProductProperty text and quantity

In `AdministrableProductProperty`, the `text` attribute is required and the `quantity` attribute is optional. This means that you always have to provide a text value, even if the property value is a quantity. Should `text` be made optional with a rule indicating that a value is expected for either `text` or `quantity`?

This question was raised in [this comment](https://github.com/cdisc-org/DDF-RA/issues/446#issuecomment-2293645983) (3rd to last bullet), but was not addressed.

Currently, the only defined terminology for `AdministrableProductProperty.type` is "pH". As it's a number, I assume the value for the "pH" property would be represented as in `quantity.value` without a unit. However, for the instance to be valid, the number would also have to be represented in `text`.