Add support for `UPDATE FORCE...`

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Normally, if an UPDATE is a no-op, i.e., if it doesn't actually change any record values, then no row data is written to the binlog. This patch adds support for UPDATE FORCE which forces row data to be written in this case. This is useful in the context of a binlog-based Change Data Capture (CDC) system in which it is sometimes desirable to snapshot a table by flushing all records through the binlogs without actually modifying anything. Feedback appreciated.