Merge branch 'master' into glitch-soc/merge-upstream

Manually-resolved conflicts:
	.circleci/config.yml
	app/controllers/accounts_controller.rb
	app/controllers/auth/passwords_controller.rb
	app/controllers/statuses_controller.rb
	app/javascript/packs/public.js
	app/models/media_attachment.rb
	app/views/stream_entries/_content_spoiler.html.haml
	app/views/stream_entries/_media.html.haml
	config/locales/en.yml
	config/locales/ja.yml
	config/locales/pl.yml
	lib/mastodon/version.rb

Some content from app/javascript/packs/public.js has been split to
app/javascript/core/settings.js.

Translation strings for glitch-soc's keyword mutes were dropped.

Everything else was mostly “take both”.

app/models/account.rb

@@ -70,6 +70,7 @@ class Account < ApplicationRecord
 
   # Remote user validations
   validates :username, uniqueness: { scope: :domain, case_sensitive: true }, if: -> { !local? && will_save_change_to_username? }
+  validates :username, format: { with: /\A#{USERNAME_RE}\z/i }, if: -> { !local? && will_save_change_to_username? }
 
   # Local user validations
   validates :username, format: { with: /\A[a-z0-9_]+\z/i }, length: { maximum: 30 }, if: -> { local? && will_save_change_to_username? }