[HttpKernel][FrameworkBundle][TwigBundle][DoctrineBridge] Escape percent signs in kernel path parameters

The container parameter bag holds values in an escaped form where a literal
percent sign is written "%%". The kernel stored raw filesystem paths, so a
project directory such as "my%2Fother%2Fbranch" was read as a reference to a
parameter named "2Fother" and every command failed.

Escaping those paths is not enough on its own: build-time consumers resolve
them through the parameter bag, which hands back the escaped form, so the
filesystem checks in the Twig, translator, validator and serializer
extensions silently found nothing. Those call sites now unescape before
touching the filesystem and escape again before handing a path back to the
container.