Provide a way for an OpenUI Document Field Extension to be able to read other field values

At the moment, an OpenUI Document Field Extension [1] can read only the specific field value through ui.document.field.getValue().

We have the following use case where we need to read the other field value, in order to properly display/select data in the specific field picker based on the other field's value:

• In StarterStore, we have a product decorator document which has two fields: one for connector selection dropdown, and the other for product ID value field.
• We want to add an OpenUI picker for the product ID field.
• But it has to read the connector selection field. For example, if 'brSM' is selected, the picker dialog needs to query products from brSM; if 'ElasticPath', it needs to query data from 'ElasticPath', and so on.
• Therefore, if the OpenUI Document Field Extension API supports a new API, like ui.document.getFieldValue(name), ui.document.getFieldNames(), or ui.document.getFieldValues(), it would be really nice for our use cases.

[1] https://documentation.bloomreach.com/library/concepts/open-ui/develop-a-document-field-extension.html