FIX: Use ILIKE for searching categories (#26619)

Full text search does not return ideal results for category dropdown.
Usually, in category dropdowns we want to search for categories as we
type. For example, while typing "theme", the dropdown should show
intermediary results for "t", "th", "the", "them" and finally "theme".
For some of these substrings (like "the"), full text search does not
return any results, which leads to an unpleasant user experience.

app/controllers/categories_controller.rb

@@ -366,13 +366,9 @@ class CategoriesController < ApplicationController
 
     categories = Category.secured(guardian)
 
-    categories =
-      categories
-        .includes(:category_search_data)
-        .references(:category_search_data)
-        .where(
-          "category_search_data.search_data @@ #{Search.ts_query(term: term)}",
-        ) if term.present?
+    if term.present? && words = term.split
+      words.each { |word| categories = categories.where("name ILIKE ?", "%#{word}%") }
+    end
 
     categories =
       (

spec/requests/categories_controller_spec.rb

@@ -1211,7 +1211,7 @@ RSpec.describe CategoriesController do
 
       queries = track_sql_queries { get "/categories/search.json", params: { term: "Notfoo" } }
 
-      expect(queries.length).to eq(5)
+      expect(queries.length).to eq(8)
 
       expect(response.parsed_body["categories"].length).to eq(1)
       expect(response.parsed_body["categories"][0]["custom_fields"]).to eq("bob" => "marley")
@@ -1247,10 +1247,11 @@ RSpec.describe CategoriesController do
       it "returns categories" do
         get "/categories/search.json", params: { term: "Foo" }
 
-        expect(response.parsed_body["categories"].size).to eq(2)
+        expect(response.parsed_body["categories"].size).to eq(3)
         expect(response.parsed_body["categories"].map { |c| c["name"] }).to contain_exactly(
           "Foo",
           "Foobar",
+          "Notfoo",
         )
       end
     end