feat(VRating): expose activeColor in item slot props

[Mo7ammedXD]

Description

Exposes activeColor in the #item slot props for VRating. The value is already
computed internally (props.activeColor ?? props.color) but was not passed through to
the slot, making it unavailable to consumers who customize the item rendering.

resolves #22273

Changes

• Added activeColor to VRatingItemSlot type definition
• Included activeColor in the itemState computed return value
• Added 3 tests covering: explicit activeColor, fallback to color, and undefined state

Markup:

<template>                                                                           
  <v-app>
    <v-container>
      <h3>activeColor exposed in slot</h3>
      <v-rating v-model="rating" active-color="blue" color="grey">                     
        <template #item="{ activeColor, color, isFilled, icon }">
          <v-icon :color="isFilled ? activeColor : color" size="large">                
            {{ icon }}                                                                 
          </v-icon>                                                                  
        </template>                                                                    
      </v-rating>                                         
                                                                                     
      <h3 class="mt-4">Fallback: no activeColor prop</h3>
      <v-rating v-model="rating" color="red">
        <template #item="{ activeColor, isFilled, icon }">                             
          <v-icon :color="isFilled ? activeColor : 'grey'" size="large">
            {{ icon }}                                                                 
          </v-icon>                                       
        </template>                                                                  
      </v-rating>                                                                      
 
      <h3 class="mt-4">No regression: default (no slot)</h3>                           
      <v-rating v-model="rating" active-color="purple" color="grey-lighten-1" />
    </v-container>                                                                   
  </v-app>                                                                             
</template>
                                                                                       
<script setup>                                            
  import { ref } from 'vue'                                                          
  const rating = ref(3)
</script>