refactor(baseDropdown): Move listeners out of toggleOptions

What does this MR do?

This MR refactors a small part of base_dropdown.vue to remove listeners from the toggleOptions that are set to v-bind.

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Thanks

Thanks @jannik_lehmann for pairing on this quick one with me.

Does this MR meet the acceptance criteria?

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Accessibility

If this MR adds or modifies a component, take a few moments to review the following:

• All actions and functionality can be done with a keyboard.
• Links, buttons, and controls have a visible focus state.
• All content is presented in text or with a text equivalent. For example, alt text for SVG, or aria-label for icons that have meaning or perform actions.
• Changes in a component’s state are announced by a screen reader. For example, changing aria-expanded="false" to aria-expanded="true" when an accordion is expanded.
• Color combinations have sufficient contrast.