bpo-44854: Add .editorconfig file to help enforce `make patchcheck` (GH-27638)

.editorconfig

@@ -0,0 +1,12 @@
+root = true
+
+[*.{py,c,cpp,h,rst,md,yml}]
+trim_trailing_whitespace = true
+insert_final_newline = true
+indent_style = space
+
+[*.{py,c,cpp,h}]
+indent_size = 4
+
+[*.yml]
+indent_size = 2