fix(1532) Array type default value should not generate SQL commands without change

[edeesis]

Description of change

Array defaulting for PostgreSQL would generate a change to the comment and the default value every time you ran typeorm migration:generate.

Example:

        await queryRunner.query(`
            COMMENT ON COLUMN "users"."array" IS NULL
        `);
        await queryRunner.query(`
            ALTER TABLE "users"
            ALTER COLUMN "array"
            SET DEFAULT '[]'
        `);

Fixes #1532

Pull-Request Checklist

• Code is up-to-date with the master branch
• npm run lint passes with this change
• npm run test passes with this change
• This pull request links relevant issues as Fixes #0000
• There are new or updated unit tests validating the change
• N/A - Documentation has been updated to reflect this change
• The new commits follow conventions explained in CONTRIBUTING.md

[AlexMesser]

Thank you for contribution, I had to put few changes to this PR:

• removed arrayCast from normalizeDefault since casting for default value is already removed in PostgresQueryRunner.loadTables() method;
• removed support for function definition in default because function syntax suppose to support raw sql, we don't have to confuse things by applying custom modifications.

[edeesis]

Awesome, thanks for merging @AlexMesser. This will save a decent amount of headache for our team. What's the general timeline for a release of this?

[pleerock]

Expect it next week.