Closes sphinx-doc#10385: Add RTL support for Sphinx themes

- Add is_rtl theme option for right-to-left text direction
- Implement automatic layout mirroring for RTL languages
- Keep code blocks in LTR direction

Author: Revisto

CHANGES.rst

@@ -111,6 +111,10 @@ Features added
 * #13326: Remove hardcoding from handling :class:`~sphinx.addnodes.productionlist`
   nodes in all writers, to improve flexibility.
   Patch by Adam Turner.
+* #10385: Add RTL (right-to-left) support for all Sphinx themes via ``is_rtl``
+  theme option. Includes automatic layout mirroring, and bidirectional text 
+  support.
+  Patch by Revisto.
 
 Bugs fixed
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