[clang] clang-format: Add IncludeSortKey option (PR #137840)

[Daan De Meyer via cfe-commits]

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@@ -152,6 +152,10 @@ struct IncludeStyle {
   /// \version 10
   std::string IncludeIsMainSourceRegex;
 
+  /// When sorting includes in each block, ignore file extensions.
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DaanDeMeyer wrote:

I added more explanation and added an example

https://github.com/llvm/llvm-project/pull/137840