[Issue 23376] Allow multi-code-point HTML entities

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23376

--- Comment #3 from Dennis <dkorpel at live.nl> ---
(In reply to Bolpat from comment #2)
> Maybe the reason for not supporting them is they’d be the only escape
> sequence to introduce multiple code-points, thus counting the number of
> code-points / code-units becomes non-trivial:

Looking at the source code, it seems like the only reason is because no one
bothered to implement it. `Lexer.escapeSequence` returns a single `dchar`, so
it would require a bit of refactoring.

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