Preserve author-added empty lines between promoted constructor properties

[TomasVotruba]

Problem

StandaloneLinePromotedPropertyFixer collapsed intentional empty lines between promoted constructor properties. After each comma, TokensNewliner::breakItems() forced exactly one newline via ensureWhitespaceAtIndex(), wiping any blank line the author added to visually group #[Autowire(...)] properties.

Example that got mangled:

public function __construct(
    private DeviceDetectorFactoryInterface $deviceDetectorFactory,

    #[Autowire(env: 'float:MAUTIC_BOT_HELPER_BOT_RATIO_THRESHOLD')]
    private float $botRatioThreshold = 0.6,
) {
}

Fix

Skip whitespace normalization after a comma when the following whitespace already contains a blank line (2+ line endings). Single-line argument lists are still broken onto standalone lines as before.

Added fixture covering empty lines between attributed promoted properties.