Issue Description

Expected Behavior

I would like not regenerate virtual columns.

Actual Behavior

When I create a virtual column, each time I type typeorm migration:generate, typeorm dropped and regenerate virtual column.

Steps to Reproduce

1. I create an entity with virtual column

@Column({
    asExpression: `CONCAT(firstname, ' ', lastname)`,
    generatedType: 'VIRTUAL',
    length: 255,
    nullable: false,
})
name: string;

2. I generate migration with typeorm migration:generate
3. I regenerate migration

And I have this ouput in my migration :

public async up(queryRunner: QueryRunner): Promise<void> {
        await queryRunner.query(
            `ALTER TABLE \`user\` CHANGE \`name\` \`name\` varchar(255) AS (CONCAT(firstname, ' ', lastname)) VIRTUAL`,
        );
}

public async down(queryRunner: QueryRunner): Promise<void> {
        await queryRunner.query(
            `ALTER TABLE \`user\` CHANGE \`name\` \`name\` varchar(255) AS CONCAT(firstname, ' ', lastname)) VIRTUAL`,
        );
}

My Environment

Relevant Database Driver(s)

Are you willing to resolve this issue by submitting a Pull Request?

• ✖️ Yes, I have the time, and I know how to start.
• ✖️ Yes, I have the time, but I don't know how to start. I would need guidance.
• ✖️ No, I don’t have the time, but I can support (using donations) development.
• ✅ No, I don’t have the time and I’m okay to wait for the community / maintainers to resolve this issue.