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)

Postgres has a `SERIAL` data type to allow shorthand for
`nextval('sequence_name')`, but DDL like this:

    CREATE TABLE example (id SERIAL)

Cannot be generated in the DBAL schema APIs.

And then we don't need to wait till v3 to not require comments on the
JsonType.

On 31d01283 we made JsonType the default
one, which caused some unexpected results with the comparator.

This tests validates that if users have a JSON column but are using the
JsonArrayType we'll just add a comment to the column.

Reference: https://github.com/doctrine/dbal/pull/2782