Bug #34893684: Alter Table IMPORT TABLESPACE crashes after upgrade

PROBLEM:

• In current version pattern for naming hidden dropped column has
  changed.
• When cfg file is taken from older version hidden dropped column
  name follows old pattern.
• When INSTANT operations are done in current version exactly in same
  order as done before creating cfg file, then the server crashes.

FIX:

• When searching dropped column with older name version returns null,
  IMPORT fails with error SCHEMA_MISMATCH.

从 Alter Table IMPORT TABLESPACE 路径以及 INSTANT 操作期间对隐藏的已删除列名称的处理开始。使用较旧的 cfg 文件重现升级场景，然后验证缺少旧模式列时会产生 SCHEMA_MISMATCH，而不是导致服务器崩溃。