Add some completion for Symfony DI

[stof]

Note sure if this should be done here, or whether the Symfony plugin should just handle them itself.

[Koc]

IMHO we should move as much more to toolbox plugin for getting support of autocomplete in projects that uses Symfony components without Symfony full-stack.

[stof]

@Koc I tend to enable the Symfony plugin on them too, to get all features (getting completion for known service ids requires the special providers implemented in the Symfony plugin, unless you want to build a json file listing all service types and all service ids in your project. Enabling the Symfony plugin is just way easier). Most autocompletion for Symfony DI cannot be moved to PHP toolbox without moving the Symfony plugin there itself.

[stof]

@Haehnchen ?