We want to enhance the existing utrecht-textbox component by wrapping it in a utrecht-textbox-container that supports leading and trailing "slots". This will allow for more flexible and customizable layouts, such as adding icons, buttons, or other elements before or after the textbox. This is a prerequisite of the work for our clippy-combobox.

Requirements:

• utrecht-textbox-container should accept two slots/properties: leading and trailing.
• utrecht-textbox should remain the primary slot/child of the container.
• The slots should be optional and not affect the core functionality of utrecht-textbox.

Anatomy

+----------------------------------------+
|  [LEADING]  |  TEXTBOX  |  [TRAILING]  |
+----------------------------------------+

• [LEADING]: Optional content (e.g., icon, button).
• [TEXTBOX]: The existing utrecht-textbox component.
• [TRAILING]: Optional content (e.g., icon or button).

Acceptance Criteria:

• utrecht-textbox-container is implemented and documented.
• The leading and trailing slots/properties are functional and optional.
• The existing utrecht-textbox functionality remains unchanged.
• The component is backward compatible.