Currently (since f3089bf3d1),
when printing a warning to the log about large rows and/or cells
the clustering key string is concatenated to the partition key string,
rendering the warning confsing and much less useful.
This patch adds a '/' delimiter to separate the fields,
and also uses one to separate the clustering key from the column name
for large cells. In case of a static cell, the clustering key is null
hence the warning will look like: `pk//column`.
This patch does NOT change anything in the large_* system
table schema or contents. It changes only the log warning format
that need not be backward compatible.
Fixes#11620
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>