Add a Date decoder to the pg adapter to type cast dates

at the connection level

Fix rails#51448

Type cast columns of type `date` to ruby `Date` when running a raw
query through `ActiveRecord::Base.connection.select_all`.

activerecord/CHANGELOG.md

@@ -1,3 +1,13 @@
+*   `PostgreSQLAdapter` now decodes columns of type date to `Date` instead of string.
+
+    Ex:
+    ```ruby
+    ActiveRecord::Base.connection
+         .select_value("select '2024-01-01'::date").class #=> Date
+    ```
+
+    *Joé Dupuis*
+
 *   Strict loading using `:n_plus_one_only` does not eagerly load child associations.
 
     With this change, child associations are no longer eagerly loaded, to

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -1159,6 +1159,7 @@ def add_pg_decoders
             "bool" => PG::TextDecoder::Boolean,
             "timestamp" => PG::TextDecoder::TimestampUtc,
             "timestamptz" => PG::TextDecoder::TimestampWithTimeZone,
+            "date" => PG::TextDecoder::Date,
           }
 
           known_coder_types = coders_by_name.keys.map { |n| quote(n) }

activerecord/test/cases/adapters/postgresql/date_test.rb

@@ -39,4 +39,10 @@ def test_bc_date_year_zero
     topic = Topic.create!(last_read: date)
     assert_equal date, Topic.find(topic.id).last_read
   end
+
+  def test_date_decoder
+    date = ActiveRecord::Base.connection.select_value("select '2024-01-01'::date")
+    assert_equal Date.new(2024, 01, 01), date
+    assert_equal Date, date.class
+  end
 end