Bug #34893684: Alter Table IMPORT TABLESPACE crashes after upgrade

[Lemonacyy]

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.

[Lemonacyy]

Upstream Reference
mysql-server@4693e78

[Lemonacyy]

PR: #98