Improves the readability of the collected arrays in the profiler.
[HttpKernel] tweaked value exporter
removed double-stringification of values in the profiler
feature #10352 [DataCollector] Improves the readability of the collected arrays in the profiler (fabpot)

This PR was merged into the 2.5-dev branch.

Discussion
----------

[DataCollector] Improves the readability of the collected arrays in the profiler

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

This PR is based on #10155.

Original description:

It simply improves the readability of the collected arrays in the profiler:

__before__:
```
Array(date => Array(year => , month => , day => ), time => Array(hour => ))
```

__after__:
```
[
  date => [
      year => ,
      month => ,
      day =>
  ],
  time => [
      hour =>
  ]
]
```

Commits
-------

dce66c9 removed double-stringification of values in the profiler
1cda2d4 [HttpKernel] tweaked value exporter
3f297ea Improves the readability of the collected arrays in the profiler.