[BenoitNorrin]

When using symfony-ux, the composer install command must be run before npm install so the JavaScript dependencies can be retrieved in the vendor/ directory.

[Frzk]

Thanks for this PR, and all my apologies for the delay.

• We've preferred to keep the current behavior and decided to introduce a new environment variable named PHP_BUILDPACK_RUN_COMPOSER_FIRST that will allow you to run Composer before npm kicks in.
  The environment variable value must be set to true.

• Regarding the support for pdo_sqlsrv, I'd be enclined to accept it if you'd put it in another PR, with an up-to-date version (5.13.3).

Thanks again for your understanding <3

Superseded by #635