feature #12820 Added the docs for the UUID polyfill (javiereguiluz)

This PR was squashed before being merged into the 3.4 branch (closes #12820).

Discussion
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Added the docs for the UUID polyfill

Commits
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fcb2b89 Added the docs for the UUID polyfill

Author: OskarStark

components/polyfill_uuid.rst

@@ -0,0 +1,57 @@
+.. index::
+    single: Polyfill
+    single: PHP
+    single: Components; Polyfill
+
+The Symfony Polyfill / UUID Component
+=====================================
+
+    This component provides ``uuid_*`` functions to users who run PHP versions
+    without the UUID extension.
+
+Installation
+------------
+
+.. code-block:: terminal
+
+    $ composer require symfony/polyfill-uuid
+
+.. include:: /components/require_autoload.rst.inc
+
+Usage
+-----
+
+Once this component is installed in your application, you can use the following
+functions, no matter if the `PHP UUID extension`_ is installed or not in your
+server.
+
+Provided Constants
+~~~~~~~~~~~~~~~~~~
+
+* ``UUID_VARIANT_NCS`` (value = 0)
+* ``UUID_VARIANT_DCE`` (value = 1)
+* ``UUID_VARIANT_MICROSOFT`` (value = 2)
+* ``UUID_VARIANT_OTHER`` (value = 3)
+* ``UUID_TYPE_DEFAULT`` (value = 0)
+* ``UUID_TYPE_TIME`` (value = 1)
+* ``UUID_TYPE_DCE`` (value = 4)
+* ``UUID_TYPE_NAME`` (value = 1)
+* ``UUID_TYPE_RANDOM`` (value = 4)
+* ``UUID_TYPE_NULL`` (value = -1)
+* ``UUID_TYPE_INVALID`` (value = -42)
+
+Provided Functions
+~~~~~~~~~~~~~~~~~~
+
+* :phpfunction:`uuid_create`
+* :phpfunction:`uuid_is_valid`
+* :phpfunction:`uuid_compare`
+* :phpfunction:`uuid_is_null`
+* :phpfunction:`uuid_type`
+* :phpfunction:`uuid_variant`
+* :phpfunction:`uuid_time`
+* :phpfunction:`uuid_mac`
+* :phpfunction:`uuid_parse`
+* :phpfunction:`uuid_unparse`
+
+.. _`PHP UUID extension`: https://pecl.php.net/package/uuid