Isolate the PHAR with PHP-Scoper

[theofidry]

• Installed PHP-Scoper as a global dependency (there is no auto-phar on release neither installers yet)
• Modified the PHAR build script to:
  • reduce the number of files to scope (e.g. avoid to scope files from dev deps) & ship (e.g. dev deps)
  • scope the content before building the PHAR
  • optimize the autoloader before building the PHAR
• Added an end to end test for the isolated PHAR: a simple schema.yml is provided with the expected files
• Commited the composer.lock: if used as a library this does not matter and the tests don't rely on it (a composer update is ran). However for shipping the PHAR, specific versions are expected. This is also required by PHP-Scoper as some patches are required and they are by nature extremely brittle. A way to avoid that would be to patch PHP-CS-Fixer directly but that's another story.

Right now the build is failing due to an error in the PHAR. However as it works with the isolated deps (e.g. if I take build/bin/schema instead of schema.phar) it works so it seems that the error is not coming from those changes.

[theofidry]

Rebased. Note that the config is very brittle. Unfortunately there is not much which can be done here or at PhpScoper level. The real fix is patching PHP-CS-Fixer to avoid those dynamic piece of codes that could be scoped more easily without patchers

[theofidry]

@dunglas R4R