QueryParam prefill, enable stateless-to-instance flow with shared data model and attachments

### Description

**Context**

We initially implemented url param data prefill with the requirement that you can only link to a stateless task. This is because we dont want to allow automatic creation of an instance with prefilled data as this is a potential security risk.

However, service owners are not happy about this as it will often require an extra step for users.

We discussed three potential solutions:

1. Do nothing – insist that a stateless step is used

2. Allow submitting data from the stateless step

3. Allow linking to stateful steps as an opt-in feature.

We concluded that alternative 2 best covers the requirements for now and in the future.

### Additional Information

Implementation:

- Should be able to transition from stateless step to submitted form (InstantiationButton or another button must also trigger process/next afterward)
- Must be able to use the same data model + layoutSet + attachments in both stateless and instance modes
- Instantiation must use createMultiPart to upload data model(s), attachments, etc.
- FileUpload must be updated to support stateless mode
- FileUploadWithTag might need to be supported? Along with multiPart support to apply tags to an attachment. Can probably be removed (and deprecate the component?)
- Data processing APIs (with validation) for multiple data models at once in stateless. Do not include attachments, but include metadata for them? Might need to include previousData + patch to make this more similar to stateful
- Anonymous stateless can mostly behave the same, but we should prevent FileUpload* and InstantiationButton from functioning there

Start by tracing the existing QueryParam prefill flow and the InstantiationButton, FileUpload, and FileUploadWithTag entry points. Read how createMultiPart and the stateless data-processing APIs currently handle models and attachments. Done means a non-anonymous stateless step can submit the shared data model, layout, and attachments, while anonymous stateless mode prevents FileUpload* and InstantiationButton use.

Written by the indexing model from the issue text.