feature #3436 [Reference][Form Types] Add missing docs for "action" and "method" option (bicpi)

This PR was merged into the 2.3 branch.

Discussion
----------

[Reference][Form Types] Add missing docs for "action" and "method" option

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | #3410

I'm not sure of adding these two options as separate rst-files because I don't think they will get listed as `inherited` options. But no other options are embedded directly. Please let me know if I can improve that.

Commits
-------

793c8a0 Add note about the PATCH method
4555495 Update note wording for "method" option
70ca6da Improvements after review
cecc762 Update "method" description
a636945 Fixes after review
83ff4b1 Improve descriptions
1bf3ce0 [Reference][Form Types] Add missing docs for "action" and "method" option

Author: weaverryan

reference/forms/types/form.rst

@@ -62,3 +62,7 @@ on all fields.
 .. include:: /reference/forms/types/options/post_max_size_message.rst.inc
 
 .. include:: /reference/forms/types/options/pattern.rst.inc
+
+.. include:: /reference/forms/types/options/action.rst.inc
+
+.. include:: /reference/forms/types/options/method.rst.inc

reference/forms/types/options/action.rst.inc

@@ -0,0 +1,12 @@
+.. versionadded:: 2.3
+    The ``action`` option was introduced in Symfony 2.3.
+
+action
+~~~~~~
+
+**type**: ``string`` **default**: empty string
+
+This option specifies where to send the form's data on submission (usually an
+URI). Its value is rendered as the ``action`` attribute of the ``form``
+element. An empty value is considered a same-document reference, i.e. the form
+will be submitted to the same URI that rendered the form.

reference/forms/types/options/method.rst.inc

@@ -0,0 +1,31 @@
+.. versionadded:: 2.3
+    The ``method`` option was introduced in Symfony 2.3.
+
+method
+~~~~~~
+
+**type**: ``string`` **default**: ``POST``
+
+This option specifies the HTTP method used to submit the form's data. Its
+value is rendered as the ``method`` attribute of the ``form`` element and is
+used to decide whether to process the form submission in the
+``handleRequest()`` method after submission. Possible values are:
+
+* POST
+* GET
+* PUT
+* DELETE
+* PATCH
+
+.. note:
+
+    When the method is PUT, PATCH, or DELETE, Symfony will automatically
+    render a ``_method`` hidden field in your form. This is used to "fake"
+    these HTTP methods, as they're not supported on standard browsers. For
+    more information, see :doc:`/cookbook/routing/method_parameters`.
+
+.. note:
+
+    Only the PATCH method allows submitting partial data without that missing
+    fields are set to ``null`` in the underlying data (preserving default
+    values, if any).