feat(VRating): expose activeColor in item slot props

[mixelburg]

Fixes #22273

Currently only color is passed to the #item slot, even though activeColor is a distinct prop that gets resolved separately. This makes it hard to use activeColor for custom rendering without manually re-deriving it from props.

The activeColor is already computed in itemState — this just includes it in the returned object so it shows up in the slot payload alongside color.

Before:

<VRating>
  <template #item="{ color, props, isFilled }">
    <!-- activeColor not available here -->
  </template>
</VRating>

After:

<VRating active-color="red" color="grey">
  <template #item="{ color, activeColor, isFilled, props }">
    <VIcon :color="isFilled ? activeColor : color" v-bind="props" />
  </template>
</VRating>

[J-Sek]

• features go to dev branch