[Form] made DefaultCsrfProvider using session_status() when available
merged branch bamarni/form-default-csrf-provider-session-status (PR #7449)

This PR was merged into the 2.1 branch.

Discussion
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[Form] made DefaultCsrfProvider using session_status() when available

| Q             | A
| ------------- | ---
| Bug fix?      | [on PHP 5.4]
| Tests pass?   | [yes]
| License       | MIT

Commits
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5afea04 [Form] made DefaultCsrfProvider using session_status() when available