Add the concept of an RCStr string - a "Reference Counted String". Use

Add the concept of an RCStr string - a "Reference Counted String".  Use
these to keep track of big JSON strings that might need to be used in
multiple places at the same time with different lifetimes.  Add two
different JSON string values to each parse - one with and one without
changes.  The net result is a large reduction in the number of parses
that occur when doing an UPDATE of a indexed JSON field using
json_replace() or similar.

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