chore(editorconfig): update to 120 characters

Also indicate max_line_length is not an official setting.

.editorconfig

@@ -7,9 +7,11 @@ end_of_line = lf
 insert_final_newline = true
 indent_size = 4
 indent_style = space
-max_line_length = 100
 trim_trailing_whitespace = true
 
+# Removed from EditorConfig spec, but still supported by some editors.
+max_line_length = 120
+
 [{*.cmake,CMakeLists.txt}]
 # TODO: indent_size = 2
 indent_size = 4