Co-authored-by: Claudio Zizza <859964+SenseException@users.noreply.github.com>

Segregated support of unique index and unique constraint. Added missing commits: 400d73c8a1e4f53459a877c8652811ee22c0913b, e91811cb3fe3101d7d8ac95c45f8bc1ba9bd913a, a4ecf053186b11bc31fbff79ef36248500383908, d7d1c397a35735383b34632d3a67bbc3a3371a45, c71b3ae0425e5c039b047825dbf8351a773e6785, 2f9da39ec645b54d08c95649c99d7b87a32bdc72 and 9aa4e79aab0477b4212b01d65de53193d9559e39

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

The failures are caused by the changes in PHP according to https://wiki.php.net/rfc/notice-for-non-valid-array-container.

This coherent with what is done for Table. All platform specific things
are grouped into an options array. Eventually flags should be migrated
into options as well.

Support for Partial Indexes was available in Doctrine 1 following
http://www.doctrine-project.org/jira/browse/DC-82. This commit
reintroduce support for Doctrine 2. We use the same syntax with an
optionnal "where" attribute for Index and UniqueConstraint.