Detect classes in markdown inline directives

[thecrypticace]

Fixes #18071

[RobinMalfait]

Just missing a changelog entry

[helpimnotdrowning]

Hi, I am currently embedding markdown in a string and passing it to an HTML converter in a .ps1 PowerShell file (not a Markdown .md file). I noticed the markdown class detector only scans .md/.mdx files for markdown classes; is it possible to have this work across any file?

My use is something like this:

@"
blah blah blah [a link](https://google.com){.no-underline!}
"@ | ConvertFrom-Markdown | % Html

which generates the following:

<p>blah blah blah <a href="https://google.com" class="no-underline!">a link</a></p>

(but only when it is sent, it is stored as PowerShell, not Markdown)

---

I can workaround this by storing the class name in a variable and using it in the string:

$no_underline = 'no-underline!'
@"
blah blah blah [a link](https://google.com){.$no_underline}
"@ | ConvertFrom-Markdown | % Html