Add .editorconfig.

See https://editorconfig.org/ for more information.

.editorconfig

+root = true
+
+[*]
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+end_of_line = lf
+
+[*.{c,cpp,h,hh,py,ts,js,java,m}]
+indent_style = space
+indent_size = 4
+
+[Makefile]
+indent_style = tab