[FrameworkBundle] Improved TemplateNameParser performance

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Performance test in symfony-standard:
```php
<?php

use Symfony\Bundle\FrameworkBundle\Templating\TemplateNameParser;

require __DIR__.'/vendor/autoload.php';
require __DIR__.'/app/AppKernel.php';

$kernel = new AppKernel('dev', true);
$kernel->boot();
$parser = new TemplateNameParser($kernel);

$time = microtime(true);

for ($i = 0; $i < 50; ++$i) {
    $parser->parse("AcmeDemoBundle:Foo:bar$i.html.twig");
}

echo "Time:   " . (microtime(true) - $time)*1000 . "ms\n";
echo "Memory: " . memory_get_peak_usage(true)/(1024*1024) . "MB\n";
```

Before:
```
Time:   3.80706787109ms
Memory: 1.5MB
```

After:
```
Time:   3.13401222229ms
Memory: 1.5MB
```