Fix filter on embedded properties

[Seb33300]

Fixes #7020 and #6379

Complementary to #7427

In order to fix this issue I had to :

1. filter config: allow storing properties with dot: by default KeyValueStore convert keys with dot to array.
2. in the form: automatically replace . by : because we can't use dot in input names

[javiereguiluz]

Thanks Sébastien! This is now merged.

After merging, I did some minor changes:

• 5edd0ab: fixed an issue in EntityRepository.php about the property name, updated a method in KeyValueStore.php and extract the : separator character into constant so if we change this in the future or have to use it in more place, we don't forget to udpdate the code in all the other places
• 9477324 added a simple test