Fix `Style/SlicingWithRange` cop (#25923)

.rubocop_todo.yml

app/lib/emoji_formatter.rb

app/lib/text_formatter.rb

app/models/account_alias.rb

app/models/domain_block.rb

app/models/email_domain_block.rb

app/models/preview_card_provider.rb

app/validators/status_length_validator.rb

...rate/20190726175042_add_case_insensitive_index_to_tags.rb

lib/active_record/batches.rb

lib/mastodon/premailer_webpack_strategy.rb

lib/tasks/repo.rake