Wasn't quite handling the cases where a closing bracket `]` was used in the value of one of the attributes.
```markdown
[chat quote=user channel="[broken]"]
```
Would not be correctly parsed because we would _greedily_ use the first `]` as the end of the tag even though it might be a valid character when inside proper quotes.
c39a4de139/app/assets/javascripts/discourse-markdown-it/src/features/bbcode-block.js (L62)
Re-wrote the `parseBBCodeTag` to properly handle the following cases
- A closing tag (aka `[/name]`) which are easy since they don't have any attributes
- An old `[quote=...]` format we used that doesn't uses quotes but still has various attributes of the form `key:value`
- All three valid BBCode opening tag formats we support
- `[name]` without any attributes
- `[name=foo]` with a default value
- `[name foo=bar]` with some attributes
Ended up having to fix/rewrite the few bbcode rules that were using the `parseBBCodeTag` function, namely `d-wrap` and `discourse-local-dates`.
While working on this, I think I also found a way to get rid the of shims we had in place so that plugins could use the `parseBBCodeTag` function.
Reference - https://meta.discourse.org/t/having-a-right-bracket-in-a-channel-name-breaks-all-quotes-from-that-channel/308439
53b3d2f0dc