use an appropriate comparison_operator for Mroonga or MySQL FTS in translated_title scriptable key.

also remove mostly duplicate definition of content_translation_title scriptable key.
full_text: update testERP5Catalog.py.
full_text: revert the change of _renderValueAsSearchText().
full text: explicitly specify ExactMatch in multiple relation field.
fixup! full text: add BooleanFullTextKey, that does 'AND' search by default.