Generic/IncrementDecrementSpacing: handle more situations

[jrfnl]

Description

Recreation of upstream PR squizlabs/PHP_CodeSniffer#3626:

The Generic.WhiteSpace.IncrementDecrementSpacing sniff, so far, only handled incrementors/decrementors when they were directly before/after the variable they apply to.

This commit enhances the sniff to also allow for finding superfluous whitespace when incrementing/decrementing a property or an array item.

Includes unit tests.

Note: I've only made this change for PHP files as JS support will be dropped anyway, so it didn't feel like a good use of my time to work on that.

Suggested changelog entry

Generic/IncrementDecrementSpacing: detect spacing issues for more complex variables

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From the conversation in the original issue:

For pre-increment, I can think of a further/future iteration for the sniff - checking whether a pre-increment is used on a static property with a fully qualified classname or namespace relative classname, but that is something I choose not to handle (yet) when I made this change last year. When that change would be added, then, yes, extra tests would be needed for pre-in/decrement.

++\ClassName::$prop;
++Relative\ClassName::$prop;
--namespace\Relative\ClassName::$prop;

The reason I did not make that change (yet) is that this would need a different patch for PHPCS 3.x vs PHPCS 4.x, which would make the merge more complex. Also see squizlabs/PHP_CodeSniffer#3041.