minor #22913 [Yaml] Deprecate tags using colon (GuilhemN)

This PR was squashed before being merged into the 3.4 branch (closes #22913).

Discussion
----------

[Yaml] Deprecate tags using colon

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no <!-- don't forget updating src/**/CHANGELOG.md files -->
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Using a colon in a tag doesn't look like yaml and causes trouble (see symfony/symfony#22878), so I propose to just deprecate these tags in favor of more consistent tags.

```yml
- !php/const:PHP_INT_MAX
- !php/object:O:30:"Symfony\Component\Yaml\Tests\A":1:{s:1:"a";s:3:"foo";}
```
would become
```yml
- !php/const PHP_INT_MAX
- !php/object O:30:"Symfony\Component\Yaml\Tests\A":1:{s:1:"a";s:3:"foo";}
```

Commits
-------

9815af3 [Yaml] Deprecate tags using colon

Author: xabbuh

Tests/Encoder/YamlEncoderTest.php

@@ -61,9 +61,9 @@ public function testContext()
         $obj = new \stdClass();
         $obj->bar = 2;
 
-        $this->assertEquals("    foo: !php/object:O:8:\"stdClass\":1:{s:3:\"bar\";i:2;}\n", $encoder->encode(array('foo' => $obj), 'yaml'));
+        $this->assertEquals("    foo: !php/object 'O:8:\"stdClass\":1:{s:3:\"bar\";i:2;}'\n", $encoder->encode(array('foo' => $obj), 'yaml'));
         $this->assertEquals('  { foo: null }', $encoder->encode(array('foo' => $obj), 'yaml', array('yaml_inline' => 0, 'yaml_indent' => 2, 'yaml_flags' => 0)));
-        $this->assertEquals(array('foo' => $obj), $encoder->decode('foo: !php/object:O:8:"stdClass":1:{s:3:"bar";i:2;}', 'yaml'));
-        $this->assertEquals(array('foo' => null), $encoder->decode('foo: !php/object:O:8:"stdClass":1:{s:3:"bar";i:2;}', 'yaml', array('yaml_flags' => 0)));
+        $this->assertEquals(array('foo' => $obj), $encoder->decode("foo: !php/object 'O:8:\"stdClass\":1:{s:3:\"bar\";i:2;}'", 'yaml'));
+        $this->assertEquals(array('foo' => null), $encoder->decode("foo: !php/object 'O:8:\"stdClass\":1:{s:3:\"bar\";i:2;}'", 'yaml', array('yaml_flags' => 0)));
     }
 }

composer.json

@@ -19,7 +19,7 @@
         "php": "^5.5.9|>=7.0.8"
     },
     "require-dev": {
-        "symfony/yaml": "~3.3|~4.0",
+        "symfony/yaml": "~3.4|~4.0",
         "symfony/config": "~2.8|~3.0|~4.0",
         "symfony/property-access": "~2.8|~3.0|~4.0",
         "symfony/http-foundation": "~2.8|~3.0|~4.0",
@@ -34,7 +34,7 @@
         "symfony/dependency-injection": "<3.2",
         "symfony/property-access": ">=3.0,<3.0.4|>=2.8,<2.8.4",
         "symfony/property-info": "<3.1",
-        "symfony/yaml": "<3.3"
+        "symfony/yaml": "<3.4"
     },
     "suggest": {
         "psr/cache-implementation": "For using the metadata cache.",