Defining size in some entities causes new migration every time you run diff

[profuel]

There's a closed report here: #1031
Though I'm sure that please remove size is not a good solution, since not every person can find this thread and learn that some sizes are default and due to a specific behavior of the compare tool, migrations are produced.

To raise a degree of the issue, we faced a complete downtime of the system, when the migration:

ALTER TABLE product CHANGE custom_id custom_id INTEGER;

since the table contains 100 M lines.

Other cases, causing permanent migration, please see table definition (all in one)

    <table name="brand_slug" idMethod="native" allowPkInsert="true">
        <column name="id_brand_slug" type="INTEGER" primaryKey="true" autoIncrement="true"/>
        <column name="slug" type="LONGVARCHAR" required="true"/>
        <column name="price" type="INTEGER" size="11" required="true"/>
        <column name="created_at" type="TIMESTAMP" size="6" required="true"/>

        <index name="index-brand_slug-slug">
            <index-column name="slug"/>
        </index>
    </table>

Please copy schema, generate diff and apply changes to the DB.
Then just generate diff again.
I'm getting:

 DROP INDEX `index-brand_slug-slug` ON `brand_slug`;
 ALTER TABLE `brand_slug`
  CHANGE `created_at` `created_at` TIMESTAMP(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
  CHANGE `price` `price` INTEGER(11) NOT NULL;
 CREATE INDEX `index-brand_slug-slug` ON `brand_slug` (`slug`);

My ideas of the way how to fix this:

1. fail generation of the diff/schema - if the size is wrongly specified.
2. ignore wrongly specified sizes.

[smhg]

This needs a PR with a failing test.

[PhilinTv]

Beta5 Justification: Painful dev UX issue that causes false diffs and even downtime. Fix can be additive or a warning.