Describe the feature and motivation

I'm using FileStorage to log data in JSON format, and is supposed to be readable. This includes numbers in double precision. However, the output is a fixed scientific notation that is very difficult to read. Example:

{
    "my_double": 5.000000000000000000e-01,
    "my_int": 5
}

What I want is this:

{
    "my_double": 0.5,
    "my_int": 5
}

I would like the possibility to set the format or precision of the output.

An optimal solution would be to get access to the underlying std::ostream (if there is one, I'm assuming C++ here) so that the user could manipulate the stream with std::setprecision() etc. A related issue is #15675.

Additional context

No response