[7.x] Added renameColumn() enum support

[nuernbergerA]

This PR adds support for tables with enum columns in migration files.

Current State

It's impossible to renameColumn() or change() column types on tables with an enum-column in your migrations.

There is also a big warning in the docs.

Solution

I just add the type to doctrines internal mapping and it works.

$schema = $connection->getDoctrineSchemaManager();
$databasePlatform = $schema->getDatabasePlatform();
$databasePlatform->registerDoctrineTypeMapping('enum', 'string');

What's still unsupported

Renaming and changing an enum column directly. I will take a look into this after this PR.

Thanks to my friend @bosske1 for working with me on this.
Also thanks to @staudenmeir who was so kind as to answer my questions.