Add aria-label support to button component

[Spark450]

Summary:

Add an aria-label property to the button component so product teams can provide a precise accessible name when the visible label alone isn’t specific enough (e.g., multiple “Save” buttons on one page)

Acceptance criteria:

• Button accepts aria-label and, if used, becomes the button's accessible name.
• If both visible text and aria-label are provided, the accessible name reflects aria-label
• Docs updated
  • Added to the component playground
  • Added to the property table

Question

Should we also consider adding aria-labelledby?

[Spark450]

Spoke to a member from the Assistive Technology working group. This member supported adding this feature to the button. The issue will be maintained in the backlog.