... as returning a "" is not a good idea as the string is supposed to be
allocated and returning a const string will cause issues.
Reported-by: Brian Carpenter
Follow-up to ed35d6590eCloses#5405
A common set of functions instead of many separate implementations for
creating buffers that can grow when appending data to them. Existing
functionality has been ported over.
In my early basic testing, the total number of allocations seem at
roughly the same amount as before, possibly a few less.
See docs/DYNBUF.md for a description of the API.
Closes#5300
