Reorganize the C# Guide around a new C# hub page (#39916)

* move specification content

Create a new TOC for the specification.
Move content to be displayed there.

Create spec landing page

* Create landing page for C# lang reference

Create a landing page for the C# language reference. Create a new TOC for the reference only.
Remove or update links to the old landing page to point at the new page.

* Incorporate compiler messages into reference

* First Hub page draft

* remove temporary links

* C# hub page, take 2

* Update what's new link

* move links

* review pass for the hub

* Try some dotnet-bot images.

* update C# dev kit link for VS Code.

* Apply suggestions from code review

Co-authored-by: Katie Savage <[email protected]>

* respond to feedback.

* Apply suggestions from code review

Co-authored-by: Genevieve Warren <[email protected]>

---------

Co-authored-by: Katie Savage <[email protected]>
Co-authored-by: Genevieve Warren <[email protected]>

Author: 3 people

.openpublishing.redirection.csharp.json

@@ -1328,6 +1328,10 @@
             "source_path_from_root": "/docs/csharp/language-reference/proposals/csharp-11.0/index.md",
             "redirect_url": "/dotnet/csharp/language-reference/proposals/csharp-11.0/static-abstracts-in-interfaces"
         },
+        {
+            "source_path_from_root": "/docs/csharp/language-reference/specifications.md",
+            "redirect_url": "/dotnet/csharp/specifications"
+        },
         {
             "source_path_from_root": "/docs/csharp/linq/create-a-nested-group.md",
             "redirect_url": "/dotnet/csharp/linq/standard-query-operators/grouping-data"

docs/csharp/fundamentals/exceptions/exception-handling.md

@@ -61,6 +61,6 @@ For more information, see [Exceptions](~/_csharpstandard/standard/exceptions.md)
 
 ## See also
 
-- [C# reference](../../language-reference/index.md)
+- [C# reference](../../language-reference/index.yml)
 - [Exception-handling statements](../../language-reference/statements/exception-handling-statements.md)
 - [using statement](../../language-reference/statements/using.md)