Introduce a constant for clang_version and migrate 19 -> 20

Author: zyv

docs/coding-style.md

@@ -13,10 +13,10 @@ Use the `clang-format` to format the code:
 $ make indent
 ```
 
-To avoid formatting differences between `clang-format` versions, we currently use `clang-format-19`. The [clang-format Python distribution](https://pypi.org/project/clang-format/) provides precompiled binaries for all major platforms:
+To avoid formatting differences between `clang-format` versions, we currently use `clang-format-{{ extra.clang_version }}`. The [clang-format Python distribution](https://pypi.org/project/clang-format/) provides precompiled binaries for all major platforms:
 
 ```shell
-$ uv tool install 'clang-format==19.*'
+$ uv tool install 'clang-format=={{ extra.clang_version }}.*'
 $ alias clang-format='uvx clang-format'
 ```
 

mkdocs.yml

@@ -12,6 +12,8 @@ extra:
   organization_url: https://github.com/MidnightCommander
   source_url: https://source.midnight-commander.org
 
+  clang_version: 20
+
   social:
     - icon: fontawesome/brands/github
       link: https://github.com/MidnightCommander