Update Deprecated Digraph Codepoints

[DavidFriant]

This commit updates the digraphs Left-Pointing Angle Bracket '</' and Right-Pointing Angle Bracket '/>' to account for the fact that the old Unicode codepoints for them (2329 and 232A, respectively) have been deprecated. As per the Miscellaneous Technical code chart, the old digraphs have been reassigned to CJK Left Angle Bracket and Right Angle Bracket (3008 and 3009) with their declarations moved to the appropriate block.

This commit also introduces the new digraphs '<[' and ']>' to represent the Mathematical Left Angle Bracket and Mathematical Right Angle Bracket (27E8 and 27E9) to replace the deprecated code points in the Technical block.

Tests have been added and, I believe, the documentation has been updated accordingly.

Note that this is the second attempt for this pull request as I closed the first due to a test failure which has now been corrected.

[chrisbra]

Let me repeat my message from the original, now closed PR #17989

I am not a big fan of silently changing the digraph characters. That might be unexpected and it does no longer correspond to RFC1345.

So not sure we should do this, other opinions?

[DavidFriant]

Re-hello,
Allow me to also copy my message from the closed pull request:

Hello, I am inclined to agree with you the silently changing digraph characters isn't ideal, but RFC1345 isn't likely to ever be updated as per Errata 4272. Without any expectation of an update, I think it is best to modernize things as best we can at least as far as properly using Unicode is concerned. Also, this conversation should likely continue on the Pull request that I haven't closed: #17990

[benknoble]

Meta: there’s no need to close a PR because a test failed: you can push new commits that will be reflected in the PR (or—preferable in many cases IMO—force-push rewritten history with any fixes you need). It can create confusion to have to follow conversations across multiple PRs.

[DavidFriant]

Meta: there’s no need to close a PR because a test failed: you can push new commits that will be reflected in the PR (or—preferable in many cases IMO—force-push rewritten history with any fixes you need). It can create confusion to have to follow conversations across multiple PRs.

Thanks! That's what I've since learned. I've been using git for years, but only recently decided to start making open source contributions, and the workflow is a bit different than what I am accustomed to. Sorry for the trouble.

More importantly, further discussion on whether or not to step away from strict adherence to RFC 1345 in favor of modernized Unicode is most welcome.

[chrisbra]

We made a few adjustments to the digraphs and added some new ones, like the Rouble and Euro sign. Let's include it.