Changed the type of `$char` in `AbstractPlatform::getTrimExpression()` from `string|false` to `?string`

1. The argument is always available since the method is only called from listTableIndexes() which requires a table name.
2. The argument itself seems a workaround and only needed to bypass the fact that the SQLiteSchemaManager violates the method contract: instead of reformatting the provided data it fetches more data from the DB schema which requires a table name. This argument should be dropped completely later.

  - fix 'Unknown database type string requested, Doctrine\DBAL\Platforms\SqlitePlatform may not support it.' error

Use a wrapped PDO Statement instead of a custom class for `pdo_sqlsrv` since `PDOSqlsrv\Statement` doesn't extend `PDOStatement` anymore.

The regression was introduced by 2b8c40d267b4ac699ea878dcca07332e1697978c.

Fixes #3060.