[Bug][a11y]: Slider editable NumberField labeled twice

[majornista]

Code of conduct

• [X] I agree to follow this project's code of conduct.

Impacted component(s)

Slider, FieldLabel, NumberField

Expected behavior

The NumberField that displays in the shadowDom for the editable variant of a Slider should only include the textContent for its label once as its aria-label.

A possible solution for this would be to deduplicate within the get labelText() method in FieldLabel, as follows:

    private get labelText(): string | undefined {
        const assignedNodes = this.slotEl.assignedNodes({ flatten: true });
        if (!assignedNodes.length) {
            return undefined;
        }
        const labelText = assignedNodes.map((node) =>
            (node.textContent || /* c8 ignore next */ '').trim()
        )
        /** deduplicate and omit empty nodes */
        .filter(
            (textContent, index, array) => (
                textContent.length && 
                array.findIndex((item) => item === textContent) === index
            )
        );
        return labelText.join(' ');
    }

Actual behavior

On https://opensource.adobe.com/spectrum-web-components/components/slider/#editable, the NumberField that displays in the shadowDom for the editable variant of a Slider repeats the textContent for its label twice in its aria-label.

Rendered <sp-number-field> element in shadowDom, where you can see aria-label=" Angle (editable) Angle (editable) " on the input, follows:

<sp-number-field id="number-field" min="0" max="360" step="1" value="180" hide-stepper="" dir="ltr" type="text" step-modifier="10" autocomplete="off" focusable="" data-dashlane-shadowhost="true" data-dashlane-observed="true">
    <!-- #shadow-root -->
      <div id="textfield">
          <!--?lit$812536239$-->
          <!--?lit$812536239$-->
          <!--?lit$812536239$-->
          <!--?lit$812536239$-->
          <!-- @ts-ignore -->
          <input class="input" type="text" aria-describedby="sp-help-text-1" aria-label=" Angle (editable)  Angle (editable) " placeholder="" autocomplete="off" inputmode="numeric" data-dashlane-rid="cde23094b63176a0" data-form-type="other">
          <!--?lit$812536239$--><!--?-->
      </div>
</sp-number-field>

Screenshots

No response

What browsers are you seeing the problem in?

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How can we reproduce this issue?

1. Go to '...'
2. Click on '....'
3. Scroll to '....'
4. Check console
5. See error

Sample code that illustrates the problem

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Logs taken while reproducing problem

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