Sent emails should be persisted between kernel reboots

[kbond]

The following doesn't currently work:

// ...some code that sends 2 emails...
// reboot kernel
$this->mailer()->assertSentEmailCount(2);

It needs to be modified to the following to work:

// ...some code that sends 2 emails...
$this->mailer()->assertSentEmailCount(2);
// reboot kernel

I believe the only way to achieve this is to add a lightweight bundle that registers a listener for MessageEvent and stores them statically (and resets them after the test). This would be similar to how zenstruck/messenger-test works.

This will also remove the requirement for the profiler to be enabled on some versions of Symfony:

mailer-test/tests/InteractsWithMailerTest.php

Lines 173 to 206 in 4b13884

	/**
	* @test
	*/
	public function profiler_must_be_enabled_after_5_2(): void
	{
	if (Kernel::VERSION_ID < 50200) {
	// profile needs to be enabled in 5.2+
	$this->markTestSkipped();
	}
	self::bootKernel(['environment' => 'no_profiler']);
	$this->expectException(\LogicException::class);
	$this->expectExceptionMessage('Mailer and/or profiling not enabled');
	$this->mailer();
	}
	/**
	* @test
	*/
	public function profiler_does_not_need_to_enabled_prior_to_5_2(): void
	{
	if (Kernel::VERSION_ID >= 50200) {
	// profile does not need to be enabled in <5.2
	$this->markTestSkipped();
	}
	self::bootKernel(['environment' => 'no_profiler']);
	self::$container->get('mailer')->send(new Email1());
	$this->mailer()->assertSentEmailCount(1);
	}

[OskarStark]

cc @silasjoisten