Support ordered lists

[tcr]

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This is slightly different than just duplicating the "bullet" tag to be something new, because it actually should change all adjacent tags to be a series of "enumerated" tags. But that would conflict with the transform logic, which would want to preserve intermediary insertions or joining of bullets into being bullet tags.

Changing a single parent tag at once (like a <ul> or <ol>) would be a more correct way to do this. I forget why that wasn't chosen except to avoid the problem of disjoint transforms not supporting being merged. But actually... that's the reason.

Also there has to be successive bullet information preserved anyway, such as when a list starts with a numeral other than 1. So it's either first bullet + all successive bullets being rendered as if they were joined on the client, or 2. supporting <ul> and <ol> and figuring out a disjoint transform fix.