feature #6765 [Contributing] [Standards] Do not use spaces inside/around offset accessors (phansys)

This PR was squashed before being merged into the 2.7 branch (closes #6765).

Discussion
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[Contributing] [Standards] Do not use spaces inside/around offset accessors

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes
| Applies to    | all
| Fixed tickets | N/A

Ref: PHP-CS-Fixer/PHP-CS-Fixer#2089

Commits
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e9fa33d [Contributing] [Standards] Do not use spaces inside/around offset accessors

Author: wouterj

contributing/code/standards.rst

@@ -176,7 +176,9 @@ Structure
   Read more at :ref:`contributing-code-conventions-deprecations`;
 
 * Do not use ``else``, ``elseif``, ``break`` after ``if`` and ``case`` conditions
-  which return or throw something.
+  which return or throw something;
+
+* Do not use spaces around ``[`` offset accessor and before ``]`` offset accessor.
 
 Naming Conventions
 ------------------