fix(validator): form supports multiple values with foo[]

[yusukebe]

Fixes #2625

This PR enables the validator to parse an array form value, such as the key is a foo[]. You should specify a key with the [] suffix for an array content.

Usage:

import { Hono } from 'hono'
import { z } from 'zod'
import { zValidator } from '@hono/zod-validator'

const app = new Hono()

const schema = z.object({
  'foo[]': z.array(z.string())
})

app.post('/', zValidator('form', schema), (c) => {
  const data = c.req.valid('form')
  const fooArray = data['foo[]']
  return c.json({
    fooArray
  })
})

export default app

Author should do the followings, if applicable

• Add tests
• Run tests
• bun denoify to generate files for Deno