[HttpFoundation] added class constants in Request for HTTP request methods
feature #11777 [HttpFoundation] added class constants in Request for HTTP request methods (phansys)

This PR was squashed before being merged into the 2.6-dev branch (closes #11777).

Discussion
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[HttpFoundation] added class constants in Request for HTTP request methods

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT
| Doc PR        | none

Also added constants for methods OPTIONS, TRACE and CONNECT according to [rfc2616](http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html).

Commits
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635e880 [HttpFoundation] added class constants in Request for HTTP request methods