feat(core-ui): Add ClearButton to CompositeSelect

[nsdeschenes]

The current CompositeSelect component doesn't seem to have an easy way to hook up clearing selections, which is understandable since there are multi-selection possibilities so to tackle this I'd like to add in a button that is styled to match that of the CompactSelect's clear button.

Example:

[TkDodo]

looks good, I just saw that in your aggregateDropdown, there are a lot of type assertions in CompositeSelect.Region. I just removed them all and there’s no error:

if (isMulti) {
  return (
    <CompositeSelect.Region
      key={groupKey}
      label={group.label}
      multiple
      options={group.options}
      value={activeValues}
      onChange={handleChange}
    />
  );
}

return (
  <CompositeSelect.Region
    key={groupKey}
    label={group.label}
    options={group.options}
    value={activeValues[0]}
    onChange={opt => handleChange([opt])}
  />
);
})}

feels like a win for simplicity?

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}