Support for Numeric code fence directives - GitHub flavor

[AdarshRawat1]

Describe

I'm working on P4 compiler documentation and I noticed that when Doxygen comes across code snippets like -

• 

It will remove the P from P4 and display the 4 with the code in HTML output like this -

• 

Screenshots

I tried adding space and lowercase, but I couldn't get it to hide the P4 from the output.

Expected behavior

Is there a way to hide this unknown directive, i.e. P4 from output. All the above mentioned ways render correctly on GitHub.
p.s. I'm not asking for the support of P4 language in Doxygen, but I want to hide the directive from the output.

Additional context

I added random characters (Alphabets Only) for directives, and it was not visible in the output [Expected Behavior]. So, I think the issue is due to the number 4.

Version

1.12.0

Zip File

Code_snippets.zip

[albert-github]

Did you try one of:

```.p4
```{p4}
```{.p4}

[albert-github]

at the moment only [A-Za-z] characters are allowed when not using curly brackets, probably numbers should be added as well

[albert-github]

I've just pushed a proposed patch, pull request #11213

[albert-github]

Code has been integrated in master on GitHub (please don't close the issue as this will be done at the moment of an official release).

[AdarshRawat1]

Did you try one of:

```.p4

This one renders correctly on github but in doxygen same issue

{p4} & .p4}

Not rendering on Github

[AdarshRawat1]

Code has been integrated in master on GitHub (please don't close the issue as this will be done at the moment of an official release).

Thank you @albert-github for the patch 🙌.