Add voters count support (#11917)

* Add voters count to polls

* Add ActivityPub serialization and parsing of voters count

* Add support for voters count in WebUI

* Move incrementation of voters count out of redis lock

* Reword “voters” to “people”

app/lib/activitypub/adapter.rb

@@ -21,6 +21,7 @@ class ActivityPub::Adapter < ActiveModelSerializers::Adapter::Base
     identity_proof: { 'toot' => 'http://joinmastodon.org/ns#', 'IdentityProof' => 'toot:IdentityProof' },
     blurhash: { 'toot' => 'http://joinmastodon.org/ns#', 'blurhash' => 'toot:blurhash' },
     discoverable: { 'toot' => 'http://joinmastodon.org/ns#', 'discoverable' => 'toot:discoverable' },
+    voters_count: { 'toot' => 'http://joinmastodon.org/ns#', 'votersCount' => 'toot:votersCount' },
   }.freeze
 
   def self.default_key_transform