Update Roslyn 4.7.0->4.9.2

[arussellk]

This PR fixes #140

Before any code changes, csharp-ls does not support C# 12:

#error version    Compiler version: '4.7.0-3.23416.9 (43b0b05c)'. Language version: default (11.0).

I updated the packages, built locally, and set my path to use the new executable:

$ dotnet build --configuration Release
$ mv csharp-language-server/src/CSharpLanguageServer/bin/Release/net8.0/CSharpLanguageServer csharp-language-server/src/CSharpLanguageServer/bin/Release/net8.0/csharp-ls
$ export PATH="/path/to/csharp-language-server/src/CSharpLanguageServer/bin/Release/net8.0:$PATH"

Now my editor reports C# 12 and the errors from preview features are gone:

#error version    Compiler version: '4.9.2-3.24129.6 (9934fb9e)'. Language version: 12.0.

[razzmatazz]

LGTM, lets get this in.