Support Testing Anything Protocol unit testing framework for TiDB

[lilinghai]

Enhancement request

TAP, the Test Anything Protocol, is a simple text-based interface between testing modules in a test harness. It decouples the reporting of errors from the presentation of the reports.
pgTAP is a unit testing framework for PostgreSQL written in PL/pgSQL and PL/SQL. It includes a comprehensive collection of TAP-emitting assertion functions, as well as the ability to integrate with other TAP-emitting test frameworks.

Maybe we can support the tap ut framework for TiDB and just use sql as code in tidb ut.