add: compilePrimary function to src/Schema/Grammar.php

[nickarellano]

There was a PR that was accepted for laravel/framework:v9.47.0 that breaks primary keys with SingleStore.

[9.x] Remove index name when adding primary key on MySQL #45515

Expected query:

create rowstore table `cache` (
  `key` text not null,
  `value` text not null,
  `expiration` int not null,
  shard key(`key`),
  primary key (`key`)
) default character set utf8mb4 collate 'utf8mb4_unicode_ci'

Actual problematic query:

create rowstore table `cache` (
  `key` text not null,
  `value` text not null,
  `expiration` int not null,
  shard key(`key`),
  alter table
    `cache`
  add
    primary key (`key`)
) default character set utf8mb4 collate 'utf8mb4_unicode_ci'

[carlsverre]

Thanks for the quick fix!