Move server shutdown translation to abstract mysql

1053 is the server shutdown error code. We see these fairly often at
GitHub when, for example, shutting down Vitess vtage processes for
maintenance. Translating the error to `ConnectionFailed` allows us to
treat these as retryable connection error, so we can reconnect and hit a
new vtage process.

This is all true regardless of whether the adapter is trilogy or mysql2
or whatever, so this commit moves the translation out into the abstract
mysql adapter.

Author: composerinteralia

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -776,6 +776,7 @@ def sync_timezone_changes(raw_connection)
         ER_DB_CREATE_EXISTS     = 1007
         ER_FILSORT_ABORT        = 1028
         ER_DUP_ENTRY            = 1062
+        ER_SERVER_SHUTDOWN      = 1053
         ER_NOT_NULL_VIOLATION   = 1048
         ER_NO_REFERENCED_ROW    = 1216
         ER_ROW_IS_REFERENCED    = 1217
@@ -804,7 +805,7 @@ def translate_exception(exception, message:, sql:, binds:)
             else
               super
             end
-          when ER_CONNECTION_KILLED, CR_SERVER_GONE_ERROR, CR_SERVER_LOST, ER_CLIENT_INTERACTION_TIMEOUT
+          when ER_CONNECTION_KILLED, ER_SERVER_SHUTDOWN, CR_SERVER_GONE_ERROR, CR_SERVER_LOST, ER_CLIENT_INTERACTION_TIMEOUT
             ConnectionFailed.new(message, sql: sql, binds: binds, connection_pool: @pool)
           when ER_DB_CREATE_EXISTS
             DatabaseAlreadyExists.new(message, sql: sql, binds: binds, connection_pool: @pool)

activerecord/lib/active_record/connection_adapters/trilogy_adapter.rb

@@ -13,7 +13,6 @@ class TrilogyAdapter < AbstractMysqlAdapter
       ER_BAD_DB_ERROR = 1049
       ER_DBACCESS_DENIED_ERROR = 1044
       ER_ACCESS_DENIED_ERROR = 1045
-      ER_SERVER_SHUTDOWN = 1053
 
       ADAPTER_NAME = "Trilogy"
 
@@ -201,12 +200,6 @@ def translate_exception(exception, message:, sql:, binds:)
           if exception.is_a?(::Trilogy::TimeoutError) && !exception.error_code
             return ActiveRecord::AdapterTimeout.new(message, sql: sql, binds: binds, connection_pool: @pool)
           end
-          error_code = exception.error_code if exception.respond_to?(:error_code)
-
-          case error_code
-          when ER_SERVER_SHUTDOWN
-            return ConnectionFailed.new(message, connection_pool: @pool)
-          end
 
           case exception
           when SocketError, IOError