Add fetch reactions by Reacterable model

[antonkomarev]

Feature request appeared in issue:

• How do I narrow down the reactor's reaction? #237

This is implementation of the Solution №1 from the discussion:

• Get reactions of the Reacterable model on concrete Reactable model #239 (comment)

High-level API (preferred)

Method \Cog\Contracts\Love\Reactant\Facades\Reactant::getReactionsBy method introduced:

public function getReactionsBy(
    Reacterable $reacterable,
): iterable;

Usage:

// Get all reactions the post received (API not changed)
$allReactionsOnPost = $post->viaLoveReactant()->getReactions();

// Get reactions the post received from the user
$userReactionsOnPost = $post->viaLoveReactant()->getReactionsBy($user);

Low-level API

Method \Cog\Contracts\Love\Reactant\Models\Reactant::getReactionsBy method introduced:

public function getReactionsBy(
    Reacter $reacter,
): iterable;

Usage:

// Get reactions the post received from the reacter user
$userReactionsOnPost = $post->getLoveReactant()->getReactionsBy($user->getLoveReacter());