minor #20307 Add BC promise rules for constructors (alexandre-daubois)

This PR was merged into the 5.4 branch.

Discussion
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Add BC promise rules for constructors

As spotted in symfony/symfony#58490, following symfony/symfony#58490 (comment)

Commits
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72d416c Add BC promise rules for constructors

Author: javiereguiluz

contributing/code/bc.rst

@@ -258,6 +258,14 @@ Make public or protected                                                  Yes
 Remove private property                                                   Yes
 **Constructors**
 Add constructor without mandatory arguments                               Yes             :ref:`[1] <note-1>`
+:ref:`Add argument without a default value <add-argument-public-method>`  No
+Add argument with a default value                                         Yes             :ref:`[11] <note-11>`
+Remove argument                                                           No              :ref:`[3] <note-3>`
+Add default value to an argument                                          Yes
+Remove default value of an argument                                       No
+Add type hint to an argument                                              No
+Remove type hint of an argument                                           Yes
+Change argument type                                                      No
 Remove constructor                                                        No
 Reduce visibility of a public constructor                                 No
 Reduce visibility of a protected constructor                              No              :ref:`[7] <note-7>`
@@ -473,6 +481,10 @@ a return type is only possible with a child type.
 constructors of Attribute classes. Using PHP named arguments might break your
 code when upgrading to newer Symfony versions.
 
+.. _note-11:
+
+**[11]** Only optional argument(s) of a constructor at last position may be added.
+
 Making Code Changes in a Backward Compatible Way
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~