fix(VSelect/VAutocomplete/VCombobox): apply menu-elevation to content

[lazerg]

Description

menu-elevation set the elevation on the VSheet inside the menu, but the visible shadow comes from .v-select__content, which gets a fixed elevation from the stylesheet. The sheet's own shadow is clipped by overflow: hidden, so the prop never had any effect. This moves the elevation class onto the menu content, where it overrides the stylesheet default.

fixes #23192

Markup:

<template>
  <v-app>
    <v-container>
      <v-select :items="['Foo', 'Bar']" :menu-elevation="0" />
    </v-container>
  </v-app>
</template>