[Feature Request] Add isMobile to expanded-item slot scope

[yariksav]

Problem to solve

In mobile view of VDataTable expanded-item slot continue set colspan to headers length, and no chance to change it

      <template v-slot:expanded-item="{ headers, item }">
        <td :colspan="headers.length">
          ...
        </td>
      </template>

Proposed solution

I suppose after adding isMobile into slot scope

vuetify/packages/vuetify/src/components/VDataTable/VDataTable.ts

Line 381 in 9ff5616

}, [this.$scopedSlots['expanded-item']!({ item, headers: this.computedHeaders })])

we can do like this

      <template v-slot:expanded-item="{ headers, item, isMobile }">
        <td :colspan="isMobile ? 1 : headers.length">
          <OrderInfoPanel :value="item" />
        </td>
      </template>

[jacekkarczmarczyk]

Could be added to other slots as well