Variable size delimiters for doubled delimiters such as ⦅ ⦆, 〚 〛, ⦃ ⦄, etc.

[topological-modular-forms]

Problem. There are many instances where variable-size doubled delimiters such as ⦅ ⦆, 〚 〛, ⦃ ⦄, etc. are needed, such as rings of formal power series $R〚t〛$, rings of formal Laurent series $R⦅t⦆$, and so on.

Design Plan. Implement an extensive set of doubled delimiters, including doubled parentheses, doubled brackets, doubled curly braces, doubled angle brackets, and whatever else is necessary.

Also consider implementing tripled brackets.