Multiple annotation patterns cause slowness

[Padam87]

https://github.com/sonata-project/SonataAdminBundle/issues/4292#issuecomment-276961138

(Major problems are fixed by https://github.com/schmittjoh/JMSDiExtraBundle/pull/271, but this is a separate issue)

When having multiple annotation patterns, the combined time to search for them can be long. The code should be changed to look for all registered patterns in one swoop.