[jack-worman]

Adds an opt-in reportRedundantVarTag parameter that reports an inline @var tag whose type PHPStan already infers (varTag.redundant). It's off by default because IDEs still rely on @var.

• The engine decides this where it applies the tag, in every pass over the statement, so a tag whose type flows back into what it re-types (through a loop, a by-reference closure, a static variable or an inferred template argument) isn't reported.
• Not reported either: a tag that changes the type, like the issue's playground example, where @var string widens 'ab'; a tag in a trait; and a tag that overrides another @var for the same variable.
• turbo-ext's native handlers call the same PHP detector, which only runs with the parameter on, so the detector has no C++ mirror.

Complements #6887 (@phpstan-ignore-var): a redundant tag the IDE still needs can be kept with it, and PHPStan then never applies it.

Closes phpstan/phpstan#5308