Enable frozen strings in lib/banzai/filter/*.rb

Excludes a few filters that require more work:

* lib/banzai/filter/image_lazy_load_filter_spec.rb
* lib/banzai/filter/syntax_highlight_filter_spec.rb
* lib/banzai/filter/table_of_contents_filter_spec.rb

Part of #47424

changelogs/unreleased/sh-freeze-banzai-filter-strings.yml

+---
+title: Enable frozen strings in lib/banzai/filter/*.rb
+merge_request: 20775
+author:
+type: performance

lib/banzai/filter/absolute_link_filter.rb

+# frozen_string_literal: true
+
 require 'uri'
 module Banzai

lib/banzai/filter/abstract_reference_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # Issues, Merge Requests, Snippets, Commits and Commit Ranges share

lib/banzai/filter/ascii_doc_post_processing_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     class AsciiDocPostProcessingFilter < HTML::Pipeline::Filter

lib/banzai/filter/autolink_filter.rb

+# frozen_string_literal: true
+
 require 'uri'
 module Banzai

lib/banzai/filter/blockquote_fence_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     class BlockquoteFenceFilter < HTML::Pipeline::TextFilter

lib/banzai/filter/color_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML filter that renders `color` followed by a color "chip".

lib/banzai/filter/commit_range_reference_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML filter that replaces commit range references with links.

lib/banzai/filter/commit_reference_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML filter that replaces commit references with links.

lib/banzai/filter/commit_trailers_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML filter that replaces users' names and emails in commit trailers

lib/banzai/filter/emoji_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML filter that replaces :emoji: and unicode with images.

lib/banzai/filter/epic_reference_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # The actual filter is implemented in the EE mixin

lib/banzai/filter/external_issue_reference_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML filter that replaces external issue tracker references with links.

lib/banzai/filter/external_link_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML Filter to modify the attributes of external links

lib/banzai/filter/gollum_tags_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML Filter for parsing Gollum's tags in HTML. It's only parses the

lib/banzai/filter/html_entity_filter.rb

+# frozen_string_literal: true
+
 require 'erb'
 module Banzai

lib/banzai/filter/image_link_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML filter that wraps links around inline images.

lib/banzai/filter/inline_diff_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     class InlineDiffFilter < HTML::Pipeline::Filter

lib/banzai/filter/issuable_reference_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     class IssuableReferenceFilter < AbstractReferenceFilter

lib/banzai/filter/issuable_state_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML filter that appends state information to issuable links.