documentation: { hidden: true } on a Hash parameter doesn't hide its nested query parameters #1015

When a hash parameter is hidden from the documentation, its nested children are
still emitted as separate parent[child] query parameters, referencing a
parameter that no longer exists in the document.

Reproduction

require 'logger' # only needed in a bare script with activesupport 6.1 on Ruby 3.x
require 'grape'
require 'grape-swagger'
require 'rack/test'
require 'json'

class API < Grape::API
  format :json

  params do
    optional :query, type: String
    optional :filters, type: Hash, documentation: { hidden: true } do
      optional :status, type: String
      optional :kind, type: String
    end
  end
  get('/search') { 'ok' }

  add_swagger_documentation
end

include Rack::Test::Methods

def app
  API
end

get '/swagger_doc'
names = JSON.parse(last_response.body).dig('paths', '/search', 'get', 'parameters').map { _1['name'] }
puts names.inspect

Actual / Expected

actual:   ["query", "filters[status]", "filters[kind]"]   # verified, grape-swagger 2.1.1
expected: ["query"]

Cause

Grape::Endpoint#params_object (reopened by grape-swagger, endpoint.rb) checks
hidden_parameter? per entry of build_request_params. Nested params arrive as
separate entries (filters[status], …) whose options don't carry the parent's
documentation, so the parent's hidden: true is never considered for them
(and the container entry itself is dropped, leaving orphaned children).
Verified on v2.1.1; the same code path is present in v2.2.0 (endpoint.rb and
RequestParamParsers::Route). We currently work around it by prepending a
module to Grape::Endpoint that rejects parent[child] entries whose parent is
marked hidden in route.params — happy to PR that as a fix if the approach
fits (note: may overlap with #999).