New sniff to align array items

[fredden]

This is a follow-up on PHPCompatibility/PHPCompatibility#1586 (comment) so the task doesn't get lost / forgotten. We would like to have a sniff to enforce alignment of array items.

The sniff Squiz.Arrays.ArrayDeclaration (with its DoubleArrowNotAligned rule) has been reviewed and found to be not suitable / robust enough in all cases. For example, see PHPCompatibility/PHPCompatibility@74fc529#diff-05ae9cddcaec1e845771a7db224961439f83ef5939ec67d3a48744cb34d7e58bR106-R110

It's not strictly necessary to create a new sniff in this repository to satisfy this requirement; if a suitable sniff in another standard can be identified, it's possible to use that here.

[jrfnl]

A sniff for this is planned to be added to the PHPCSExtra NormalizedArrays ruleset. Once that ruleset is completely done, the Squiz.Arrays.ArrayDeclaration sniff will be removed from PHPCSDevCS and replaced by the NormalizedArrays standard (with potentially some customization via properties).

There is no intention to add any sniffs to PHPCSDevCS itself. That will only change if at some point the need for a 100% PHPCS sniff writing specific sniff would be identified.