Reworked type-based and conditions and clarified some types to justify the ones that remain unchanged.

Closes #3187.

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

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.

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

array_merge will not work with any iterable

This reverts commit e3ab1276, reversing
changes made to f988b0a6.