full text: not DELETE many and INSERT some, but REPLACE some and DELETE others.

also update catalog_full_text table synchronously with a deferred connection.
fixup! use TokenBigramSplitSymbolAlpha parser and MroongaBooleanFullText search key.
full text: add a comment to explain current limitation in _renderValueAsSearchText();
fixup! use TokenBigramSplitSymbolAlpha parser and MroongaBooleanFullText search key.