The reasoning behind this is to essentially rely on a single type (or
the absence of it), therefore add type declarations.

Since these are private methods we can do that without breaking BC.

- 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.

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

Added upgrade notice about BC break.
Cleanups

Changed DBALException::invalidPlatformSpecified() exception to be more detailed about what was given.

Fixed cs issues

#2794 adding tests verifying the regression, `DateTimeImmutable` should STILL work, even if unintentionally

Since it was deprecated.

If you pass a null to the where array of update or delete it's
pretty obvious what you want.

Most (all?) databases won't match anything if you actually try
to compare with NULL making this a silent failure without it.

1. Reworked the parser syntax to use proper Oracle escaping syntax as '' instead of \'.
2. Moved valid tests to the Functional section to ensure correct SQL syntax and logic.

Closes #1882