[DI] Autodiscover PhpParserNodeMapper via most-specific match

[TomasVotruba]

Second of three parallel experiments removing order-sensitive registerTagged() collections in favor of autodiscover().

PhpParserNodeMapper matched by first is_a() match in registration order, so FullyQualifiedNodeMapper had to be registered before NameNodeMapper (FullyQualified extends Name) and StringNodeMapper before ExprNodeMapper (String_ extends Expr). autodiscover() filesystem order does not honor that.

Fix removes the order dependency: the consumer picks the most specific matching mapper (deepest node type), so order stops mattering.

foreach ($this->phpParserNodeMappers as $phpParserNodeMapper) {
    $nodeType = $phpParserNodeMapper->getNodeType();
    if (! is_a($node, $nodeType)) {
        continue;
    }
    // a mapper for a child node wins over one for its parent, regardless of registration order
    if ($matchedNodeType === null || is_a($nodeType, $matchedNodeType, true)) {
        $matchedNodeType = $nodeType;
        $matchedNodeMapper = $phpParserNodeMapper;
    }
}

PHP_PARSER_NODE_MAPPER_CLASSES collapses to one autodiscover() call.

Verified directly:

Node	Resolves to
FullyQualified	FullyQualifiedObjectType (not the generic Name mapper)
String_	StringType (not the Expr mapper)
Name	MixedType

Interface added to the class-leak skip list.