[code-format] Also include libc++ extensionless headers and .inc and .cppm (#73142)

These headers were skipped by the job because they didn't have an
extension. However, such headers are extremely common in libc++.

As a drive-by change, also include `.cppm` and `.inc` extensions since
those are also common in libc++.

Author: ldionne

llvm/utils/git/code-format-helper.py

@@ -126,13 +126,18 @@ def should_be_excluded(self, path: str) -> bool:
             return True
         return False
 
+    def should_include_extensionless_file(self, path: str) -> bool:
+        return path.startswith("libcxx/include")
+
     def filter_changed_files(self, changed_files: list[str]) -> list[str]:
         filtered_files = []
         for path in changed_files:
             _, ext = os.path.splitext(path)
-            if ext in (".cpp", ".c", ".h", ".hpp", ".hxx", ".cxx"):
+            if ext in (".cpp", ".c", ".h", ".hpp", ".hxx", ".cxx", ".inc", ".cppm"):
                 if not self.should_be_excluded(path):
                     filtered_files.append(path)
+            elif ext == "" and self.should_include_extensionless_file(path):
+                filtered_files.append(path)
         return filtered_files
 
     def format_run(