[Filesystem] symlink use RealPath instead LinkTarget
bug #12761 [Filesystem] symlink use RealPath instead LinkTarget (aitboudad)

This PR was squashed before being merged into the 2.3 branch (closes #12761).

Discussion
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[Filesystem] symlink use RealPath instead LinkTarget

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

Commits
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a8b8d33 [Filesystem] symlink use RealPath instead LinkTarget
Merge branch '2.3' into 2.5

* 2.3:
  [SecurityBundle] Firewall providers building - code cleaning
  [Filesystem] symlink use RealPath instead LinkTarget
  Fixed the AuthenticationProviderInterface alignment
  Fixed the proxy-manager version constraint

Conflicts:
	composer.json
	src/Symfony/Bridge/ProxyManager/composer.json