New functionality for cformat (#7893)

Fixing complexity

remove lambda

PR review fixes #1

Removing unneccesary string substitution

Handle -a and specified files

Complexity rewrite, use pathlib

lib/python/qmk/path.py

@@ -68,3 +68,17 @@ def normpath(path):
         return Path(path)
 
     return Path(os.environ['ORIG_CWD']) / path
+
+
+def c_source_files(dir_names):
+    """Returns a list of all *.c, *.h, and *.cpp files for a given list of directories
+
+    Args:
+
+        dir_names
+            List of directories, relative pathing starts at qmk's cwd
+    """
+    files = []
+    for dir in dir_names:
+        files.extend(file for file in Path(dir).glob('**/*') if file.suffix in ['.c', '.h', '.cpp'])
+    return files