DEV: Introduce enabled? API to hashtag data sources (#22632)

We need a nice way to only return some hashtag data
sources based on various site settings. This commit
adds an enabled? method that every hashtag data source
must implement. If this returns false the data source
will not be used at all for hashtag lookups or search.

plugins/chat/spec/lib/chat/channel_hashtag_data_source_spec.rb

@@ -32,6 +32,18 @@ RSpec.describe Chat::ChannelHashtagDataSource do
     Group.refresh_automatic_groups!
   end
 
+  describe "#enabled?" do
+    it "returns false if public channels are disabled" do
+      SiteSetting.enable_public_channels = false
+      expect(described_class.enabled?).to eq(false)
+    end
+
+    it "returns true if public channels are disabled" do
+      SiteSetting.enable_public_channels = true
+      expect(described_class.enabled?).to eq(true)
+    end
+  end
+
   describe "#lookup" do
     it "finds a channel by a slug" do
       result = described_class.lookup(guardian, ["random"]).first
@@ -79,11 +91,6 @@ RSpec.describe Chat::ChannelHashtagDataSource do
       Group.refresh_automatic_groups!
       expect(described_class.lookup(Guardian.new(user), ["random"])).to be_empty
     end
-
-    it "returns an empty array if public channels are disabled" do
-      SiteSetting.enable_public_channels = false
-      expect(described_class.lookup(guardian, ["random"])).to eq([])
-    end
   end
 
   describe "#search" do
@@ -149,11 +156,6 @@ RSpec.describe Chat::ChannelHashtagDataSource do
       Group.refresh_automatic_groups!
       expect(described_class.search(Guardian.new(user), "rand", 10)).to be_empty
     end
-
-    it "returns an empty array if public channels are disabled" do
-      SiteSetting.enable_public_channels = false
-      expect(described_class.search(guardian, "rand", 10)).to eq([])
-    end
   end
 
   describe "#search_without_term" do
@@ -182,11 +184,6 @@ RSpec.describe Chat::ChannelHashtagDataSource do
       )
     end
 
-    it "returns an empty array if public channels are disabled" do
-      SiteSetting.enable_public_channels = false
-      expect(described_class.search_without_term(guardian, 5)).to eq([])
-    end
-
     it "does not return channels the user does not have permission to view" do
       expect(described_class.search_without_term(guardian, 5).map(&:slug)).not_to include("secret")
     end