Use idx_ instead of ix_ for index prefix

Followup: rails#47753

Author: byroot

activerecord/CHANGELOG.md

@@ -12,7 +12,7 @@
 
     After (short format):
     ```
-    ix_on_foo_bar_first_name_last_name_administrator_5939248142
+    idx_on_foo_bar_first_name_last_name_administrator_5939248142
     ```
 
     The short format includes a hash to ensure the name is unique database-wide.

activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

@@ -1521,7 +1521,7 @@ def generate_index_name(table_name, column)
 
           # Fallback to short version, add hash to ensure uniqueness
           hashed_identifier = "_" + OpenSSL::Digest::SHA256.hexdigest(name).first(10)
-          name = "ix_on_#{Array(column) * '_'}"
+          name = "idx_on_#{Array(column) * '_'}"
 
           short_limit = max_index_name_size - hashed_identifier.bytesize
           short_name = name.mb_chars.limit(short_limit).to_s

activerecord/test/cases/migration/index_test.rb

@@ -105,7 +105,7 @@ def test_add_index_with_if_not_exists_matches_exact_index
 
       def test_add_index_fallback_to_short_name
         connection.add_index(table_name, [:foo, :bar, :first_name, :last_name, :administrator])
-        assert connection.index_name_exists?(table_name, "ix_on_foo_bar_first_name_last_name_administrator_5939248142")
+        assert connection.index_name_exists?(table_name, "idx_on_foo_bar_first_name_last_name_administrator_5939248142")
       end
 
       def test_remove_index_which_does_not_exist_doesnt_raise_with_option