Aspnetcore.docs: Add better support for Razor syntax highlighting

[Matthew-Bonner]

Highlight js currently has aspx-csharp and cshtml.

I'm not sure what the difference is between the two but neither highlight Razor syntax very well.

This is what I get in Visual Studio:

This is what I get in the docs:

[guardrex]

@vicancy Is this a DocFX issue, or is it an implementation issue on the repo side of things?

[scottaddie]

The aspx-csharp option sounds like it supports Web Forms syntax highlighting. cshtml is definitely what we want to use.

Pinging @adkinn to comment.

[vicancy]

Adding @superyyrrzz to take a look.

[adkinn]

@scottaddie yes, we're supporting Web Forms right now. Adding cshtml highlighting is in our backlog.

[scottaddie]

Closing this issue, since it's already an item on the engineering team's backlog.