boost_phrase should split by sentence of various length if we want to catch synonyms

[alexgarel]

while search?q=organically grown&boost_phrase=1 finds items with label en:organic (which has organically grown as synonym),
q=organically grown plants&boost_phrase=1 does not work.

This is because The PhraseBoostTransformer groups all the words in a phrase. If we want synonyms to be detected, we would need to group terms 2 by 2, 3 by 3, 4 by 4 etc. so that organically grown plants,
results in adding "organically grown" OR "grown plants" OR "organically grown plants"

See the deactivated test in test_search.py