Persistent surround sub-mode

[Zoybean]

Use case: I want to be able to surround a selection with a sequence of (possibly different) delimiters, e.g.:

selection: abc
goal: { [(abc)] }

currently, I do this with ms(ms[ms ms{, which is almost easier to do without the ms subcommand.
I would like to be able to do this with a dedicated sub-mode. I don't want to bikeshed keymapping, but as an example, it could be mS:

the command would therefore be: mS([ { followed by escape.
broken down step by step:

selection: abc
press mS: enters persistent surround mode
press (
selection: (abc)
press [
selection: [(abc)]
press
selection: [(abc)]
press {
selection: { [(abc)] }
press escape: back in normal mode

Note that at each step, the selection contains the added delimiters, like the ms subcommand does.

There could also be a use-case for a surround-insert mode, which keeps the selection around the inner text, and as a consequence the delimiters are added in the reverse order. However I don't think there would be a need to have both, and I find the former version more intuitive, especially as it mirrors the existing ms behaviour.

Note that this is distinct from #4825, which is just for repeating the same surround (e.g. abc -> [abc] -> [[abc]] -> [[[abc]]])