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

[Björn Schäpers via cfe-commits]

================
@@ -1647,7 +1647,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.SeparateDefinitionBlocks = FormatStyle::SDS_Leave;
   LLVMStyle.ShortNamespaceLines = 1;
   LLVMStyle.SkipMacroDefinitionBody = false;
-  LLVMStyle.SortIncludes = {/*Enabled=*/true, /*IgnoreCase=*/false};
+  LLVMStyle.SortIncludes = {/*Enabled=*/true, /*IgnoreCase=*/false, /*IgnoreExtension=*/false};
----------------
HazardyKnusperkeks wrote:

Currently it wouldn't change anything until the option is enabled. For me this change is good, I did just not vote, because of @mydeveloperday request for changes.

And as cleared, the the "wrong" sorting was due using `A.cpp` as filename and thus `A.h` becomes the main header and is put up front.

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