support tracing of array of primitive types

For example, if we add integers to Json_writer_array, they are printed in the trace the following way: -

"rec_per_key": ["1"].
"rec_per_key": ["2", "3"].

However, in the case of Json_writer_object, when a single integer is added, it is printed as
"rec_per_key": 1

It would be better to have support for tracing array of primitive types without any wrapped quotes around the values such as

"rec_per_key": [2, 3, 4 ....].