Fixes #3336.

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.

This reverts commit e3ab1276, reversing
changes made to f988b0a6.

We prefer to test across all platforms at once with
`SchemaManagerFunctionalTestCase::testEscapedDefaultValueMustBePreserved()`
rather than to test only a single specific platform.

I am not sure if there is a rationale behind ignoring extra keys like
this. I was under the impression that something might copy options to
platform specific options, thus leaving options in the original array,
knowing they would be ignored anyway. If it is the case, it would be
best to just move them, otherwise, this commit might help troubleshoot
some mapping issues.
I had to fix some tests that wrongly used that options array (maybe
these options were valid at some point?).

- SERIAL and BIGSERIAL are not true types and can't be used in ALTER TABLE expressions
- When changing between int and bigint auto increment fields the default should no be dropped
  to preserve the link between the column and the sequence.

Since the JSON type is simply an alias to a LONG TEXT we must force
a comment, otherwise things will not work properly.

Also the test for JSON types should work regardless of native JSON
support (DBAL should add a comment to identify the correct type).

Unescaping re-added, support limited to schema introspection (#2850 will bring more complete coverage)