Support HTML in Markdown strings.

[RokeJulianLockhart]

Per https://github.com/orgs/mermaid-js/discussions/5329#discussioncomment-8646264, this should be possible, yet all I see is “Unsupported Markdown: [code, break, etc.]”.

[RokeJulianLockhart]

#246 (comment)

This also appears at mermaid-js/mermaid-live-editor#1411 (comment), so like #245 (comment), this may be better reported at https://github.com/mermaid-js/mermaid/issues/new?assignees=&labels=Status%3A+Triage%2CType%3A+Bug+%2F+Error&projects=&template=bug_report.yml.

[mjbvz]

Please share the source text of example diagram that demonstrates the issue

[RokeJulianLockhart]

#246 (comment)

@mjbvz, I did provide an example in the linked issues, but I understand you not wanting to trawl through them:

```mermaid
flowchart TD
    test["`*test*<br>`"]
```

which renders as

in code-insiders-1.91.0-1718700915.el8.rpm.