Enhancement: use schema test helper to new the events used in the unit test

[3AceShowHand]

Backgroud

At the moment, we mock the event, both model.RowChangedEvent and model.DDLEvent by filling fields arbitrarily, which are used in the unit tests, spread over the codebase, it has some drawbacks:

• the event content may be wrong, does not meet SQL constraints.
• mock the event by handle is verbose and annoy

The entry.SchemaTestHelper is a test framework based upon the mock TiDB, it supports we can generate DDL and Basic Insert Event by writing SQL, which has the following advantages:

• All events are generated automatically, following SQL constraints, with no content errors.
• It makes the unit test easier to read and write.

Tasks

• open-protocol unit test embrace schema test helper #10910
• canal-json unit test embrace schema test helper #10913
• avro unit test simplification and use schema test helper #11014
• csv and maxwell unit test use schema test helper #11225