First Unique Key in a keyless table should be represented as a primary key

[VinaiRachakonda]

The following create table statement should parse

create table t(pk int not null auto_increment, UNIQUE KEY pk (pk));

[VinaiRachakonda]

We can parse this statement but we are still treating pk as UNIQUE key instead of a PRIMARY key.

Skipped bats here #4014.

[jycor]

Update: This PR dolthub/go-mysql-server#2467 fixes many issues related to this.

However, due to the way we store/retrieve indexes there are still some edge cases.