[Feature Request]: Preselect current field in dropdowns and add type-to-filter for editable lists

### What would you like to happen?

In transforms such as REST client, configuration fields like URL field name, Method field name, and Body field name show a dropdown listing available input fields. In other dialogs (e.g., Select & Alter), the field selector also exposes a list of fields.

Problem

When opening a dropdown, the list does not reliably preselect the value already configured (e.g., endpoint_api), forcing the user to scan the list.

In dropdowns that allow typing (editable combobox), typing does not consistently filter the list in real time, slowing selection in large schemas.

Goal
Improve usability and speed by:

Automatically highlighting/selecting the currently configured field when the dropdown opens.

Filtering options as the user types in any editable dropdown that lists fields.

### Issue Priority

Priority: 3

### Issue Component

Component: Hop Gui

Start with the Hop Gui dropdowns in the REST client transforms and the Select & Alter field selector described in the issue. Check how a configured field such as endpoint_api is selected when the list opens, then verify that editable field lists filter while typing; done means both behaviors work consistently across these dialogs.

Written by the indexing model from the issue text.