DEV: Remove enable_experimental_hashtag_autocomplete logic (#22820)

This commit removes any logic in the app and in specs around
enable_experimental_hashtag_autocomplete and deletes some
old category hashtag code that is no longer necessary.

It also adds a `slug_ref` category instance method, which
will generate a reference like `parent:child` for a category,
with an optional depth, which hashtags use. Also refactors
PostRevisor which was using CategoryHashtagDataSource directly
which is a no-no.

Deletes the old hashtag markdown rule as well.

spec/services/hashtag_autocomplete_service_spec.rb

@@ -313,53 +313,6 @@ RSpec.describe HashtagAutocompleteService do
     end
   end
 
-  describe "#lookup_old" do
-    fab!(:tag2) { Fabricate(:tag, name: "fiction-books") }
-
-    it "returns categories and tags in a hash format with the slug and url" do
-      result = service.lookup_old(%w[the-book-club great-books fiction-books])
-      expect(result[:categories]).to eq({ "the-book-club" => "/c/the-book-club/#{category1.id}" })
-      expect(result[:tags]).to eq(
-        {
-          "fiction-books" => "http://test.localhost/tag/fiction-books",
-          "great-books" => "http://test.localhost/tag/great-books",
-        },
-      )
-    end
-
-    it "does not include categories the user cannot access" do
-      category1.update!(read_restricted: true)
-      result = service.lookup_old(%w[the-book-club great-books fiction-books])
-      expect(result[:categories]).to eq({})
-    end
-
-    it "does not include tags the user cannot access" do
-      Fabricate(:tag_group, permissions: { "staff" => 1 }, tag_names: ["great-books"])
-      result = service.lookup_old(%w[the-book-club great-books fiction-books])
-      expect(result[:tags]).to eq({ "fiction-books" => "http://test.localhost/tag/fiction-books" })
-    end
-
-    it "handles tags which have the ::tag suffix" do
-      result = service.lookup_old(%w[the-book-club great-books::tag fiction-books])
-      expect(result[:tags]).to eq(
-        {
-          "fiction-books" => "http://test.localhost/tag/fiction-books",
-          "great-books" => "http://test.localhost/tag/great-books",
-        },
-      )
-    end
-
-    context "when not tagging_enabled" do
-      before { SiteSetting.tagging_enabled = false }
-
-      it "does not return tags" do
-        result = service.lookup_old(%w[the-book-club great-books fiction-books])
-        expect(result[:categories]).to eq({ "the-book-club" => "/c/the-book-club/#{category1.id}" })
-        expect(result[:tags]).to eq({})
-      end
-    end
-  end
-
   describe "#lookup" do
     fab!(:tag2) { Fabricate(:tag, name: "fiction-books") }
 

spec/services/post_alerter_spec.rb

@@ -1332,8 +1332,7 @@ RSpec.describe PostAlerter do
       expect(JSON.parse(body)).to eq(payload)
     end
 
-    it "does not have invalid HTML in the excerpt when enable_experimental_hashtag_autocomplete is enabled" do
-      SiteSetting.enable_experimental_hashtag_autocomplete = true
+    it "does not have invalid HTML in the excerpt" do
       Fabricate(:category, slug: "random")
       Jobs.run_immediately!
       body = nil