(C#) Support digit separators

[mgirolet-gl]

Describe the issue
Digit separators are not supported: if you write 20_000_000 for example, 20 will be number-colored, while _000_000 will be treated as invalid.

Which language seems to have the issue?
C#

Are you using highlight or highlightAuto?
highlight

Sample Code to Reproduce

int i = 20_000_000;

Expected behavior
the entirety of the number to be highlighted as a number, like on GitHub:

Additional context
None

[joshgoebel]

Thanks for the report, should be an easyish fix if you want to try your hand at a PR.

[te-ing]

I’ve opened a PR addressing this issue: [#4280 ].