Add vue/no-dupe-v-else-if rule

[ota-meshi]

This PR adds vue/no-dupe-v-else-if rule.

vue/no-dupe-v-else-if rule disallows duplicate conditions in the same v-if / v-else-if chain.

<template>
  <!-- ✗ BAD -->
  <div v-if="isSomething(x)" />
  <div v-else-if="isSomething(x)" />

  <!-- ✓ GOOD -->
  <div v-if="isSomething(x)" />
  <div v-else-if="isSomethingElse(x)" />
</template>

this rule was inspired by no-dupe-else-if rule.