Allow to implement custom taint type classes

[ohader]

Instead of just having a generic TaintedCustom for custom taint - this change allows plugins/extensions to register their own custom taint type classes.

Examples

$registry = Config::getInstance()->taint_kind_registry;

$registry->defineKinds([
  'mine' => \Example\Package\TaintedMine::class,
  'yours' => \Example\Package\TaintedYours::class,
], TaintKindGroup::GROUP_INPUT);

$registry->defineGroup('my-input', 'html', 'sql', 'shell');

$registry->defineGroupProxy('input-sql', 'input', [
  'sql' => \Example\Package\TaintedSqlSecondOrder::class,
]);

$registry->getKind('html'); // returns TaintedHtml::class;
$registry->getGroupKinds('input'); // returns ['html', 'sql', ...]

Fixes: #9186

---

TODO

• Extend input in TaintKindGroup
• Add documentation & examples for custom taint type classes

[ohader]

The failing BC tests are handled code-wise in those methods

• Psalm\Codebase#addTaintSource()
• Psalm\Codebase#addTaintSink()

[weirdan]

Perhaps move it out of Psalm/Issue namespace?

[ohader]

I'm undecided here... TaintTypeFactory creates those TaintedInput instances and probably should stay in the same namespace. However, the TaintTypeRegistry is closer to Psalm\Config and might be moved up as Psalm\TaintTypeRegistry. What do you think?