Closes #3187.

1. Use the actual dsdriver distribution
2. Introduced `AbstractPlatform::getCharMaxLength()` since `CHAR` and `VARCHAR` limitations are different on DB2.

If a PRIMARY KEY field is defined in sqlite without autoincrement then
keys might be reused when rows are deleted, explicitly settings autoincrement
will prevent this.

Autoincrement is not enabled by default due to additional overhead introduced
with autoincrement bookkeeping and should only be enabled when the additional
uniqueness is required.

For testing purposes and not only, it may be needed to evaluate an arbitrary SQL expression (see https://github.com/doctrine/dbal/pull/3013, https://github.com/doctrine/dbal/pull/3108). Instead of doing `str_replace()` on an expected string, one could specify the expression explicitly.

The SQLite and Oracle platforms produces a `ROUND()`'ed or `TRUNC()`'ated difference between the datetimes. However it should be the difference between dates.

A string is made of characters, an array might contain anything.

array_merge will not work with any iterable

The docs only talk about 2008 and up, not sure if those should be added
to 2005 too.

Inherit table charset/collation from db charset

This reverts commit e3ab1276, reversing
changes made to f988b0a6.

It is now possible to use `\` in non-escaped default values for a column,
and it will be automatically escaped for platforms that need it.

Previously this lead to a confusion when diffing actual and expected
schema leading to perpetual out of sync schema.

Before:

```php
/**
 * @ORM\Column(options={"default" = "Foo\\Bar"}))
 */
private $name;

```

After:

```php
/**
 * @ORM\Column(options={"default" = "Foo\Bar"}))
 */
private $name;

```

And the result in database will be a default value exactly as written in
the annotation, that is `Foo\Bar`.