fixed output of bag values

Call json_encode with flags: JSON_UNESCAPED_SLASHES and
JSON_UNESCAPED_UNICODE
merged branch pvolok/fix_7540 (PR #7643)

This PR was submitted for the master branch but it was merged into the 2.2 branch instead (closes #7643).

Discussion
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[WebProfilerBundle] fixed output of bag values

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7540
| License       | MIT
| Doc PR        | -

Call json_encode with flags: JSON_UNESCAPED_SLASHES and
JSON_UNESCAPED_UNICODE

Commits
-------

7ee8b10 [WebProfilerBundle] fixed output of bag values