bug #16294 [PropertyAccess] Major performance improvement (dunglas)
bug #16294 [PropertyAccess] Major performance improvement (dunglas)

This PR was squashed before being merged into the 2.3 branch (closes #16294).

Discussion
----------

[PropertyAccess] Major performance improvement

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #16179
| License       | MIT
| Doc PR        | n/a

This PR improves performance of the PropertyAccess component of ~70%.

The two main changes are:

* caching the `PropertyPath` initialization
* caching the guessed access strategy

This is especially important for the `ObjectNormalizer` (Symfony Serializer) and the JSON-LD normalizer ([API Platform](https://api-platform.com)) because they use the `PropertyAccessor` class in large loops (ex: normalization of a list of entities).

Here is the Blackfire comparison: https://blackfire.io/profiles/compare/c42fd275-2b0c-4ce5-8bf3-84762054d31e/graph

The code of the benchmark I've used (with Symfony 2.3 as dependency):

```php
<?php

require 'vendor/autoload.php';

class Foo
{
    private $baz;
    public $bar;

    public function getBaz()
    {
        return $this->baz;
    }

    public function setBaz($baz)
    {
        $this->baz = $baz;
    }
}

use Symfony\Component\PropertyAccess\PropertyAccess;

$accessor = PropertyAccess::createPropertyAccessor();

$start = microtime(true);

for ($i = 0; $i < 10000; ++$i) {
    $foo = new Foo();
    $accessor->setValue($foo, 'bar', 'Lorem');
    $accessor->setValue($foo, 'baz', 'Ipsum');
    $accessor->getValue($foo, 'bar');
    $accessor->getValue($foo, 'baz');
}

echo 'Time: '.(microtime(true) - $start).PHP_EOL;
```

This PR also adds an optional support for Doctrine cache to keep access information across requests and improve the overall application performance (even outside of loops).

Commits
-------

284dc75 [PropertyAccess] Major performance improvement

symfony/PropertyAccess,symfony/property-access