Enable support for file uploads that contain spaces

Problem/Motivation

File uploads that contains spaces return an error message that the file is not valid.

Steps to reproduce

1. Install json_form_widget.
2. Create a JSON Form field on a content type.
3. Use a schema that defines a property with "format": "uri". # Do this so it's DKAN agnostic
4. In the widget, type a filename with a space into that field (e.g., "I want to upload this file.pdf").
Attempt to save the node.
Result: The field displays an "Invalid URL" error and prevents saving.

Proposed resolution

Update the valueHandler() to look for fields that represent generic URL/URI, Drupal internal stream wrappers like "public://", "private://", or schema definitions that use uri, url, or data-url formats.

Remaining tasks

Review merge request, which hopefully resolves or at least creates a muse for the solution to this specific issue.
Test this with your own use application and use case.

User interface changes

MR includes a plugin so that you can easily assign the JSON Form Widget to a field in a content type.

API changes

None.

Data model changes

URL and URI strings will now be stored in their encoded formats (""%20") first instead of actual spaces.