feat(VSlideGroup): add content class to VSlideGroup props (#21431)

Author: jcjp

packages/api-generator/src/locale/en/VSlideGroup.json

@@ -1,6 +1,7 @@
 {
   "props": {
     "centerActive": "Forces the selected component to be centered.",
+    "contentClass": "Adds classes to the slide group item.",
     "direction": "Switch between horizontal and vertical modes.",
     "mobileBreakpoint": "Sets the designated mobile breakpoint for the component.",
     "nextIcon": "The appended slot when arrows are shown.",

packages/docs/src/data/new-in.json

@@ -124,6 +124,11 @@
       "end": "3.2.0"
     }
   },
+  "VSlideGroup": {
+    "props": {
+      "contentClass": "3.9.0"
+    }
+  },
   "VSnackbar": {
     "props": {
       "timer": "3.4.0",

packages/vuetify/src/components/VSlideGroup/VSlideGroup.tsx

@@ -50,6 +50,7 @@ type VSlideGroupSlots = {
 
 export const makeVSlideGroupProps = propsFactory({
   centerActive: Boolean,
+  contentClass: null,
   direction: {
     type: String as PropType<'horizontal' | 'vertical'>,
     default: 'horizontal',
@@ -425,7 +426,10 @@ export const VSlideGroup = genericComponent<new <T>(
         <div
           key="container"
           ref={ containerRef }
-          class="v-slide-group__container"
+          class={[
+            'v-slide-group__container',
+            props.contentClass,
+          ]}
           onScroll={ onScroll }
         >
           <div