C# Support: Add treesitter and OmniSharp LSP support (#6908)

This PR adds the C# tree-sitter grammar. It also adds OmniSharp-Roslyn
for LSP support.

Resolves issue
[#5299](https://github.com/zed-industries/zed/issues/5299)

Release Notes:

- Added C# support

## VSCode
<img width="984" alt="vscode"
src="https://github.com/zed-industries/zed/assets/6967829/1f6b4cb7-4e00-4d61-8e58-2867dc5c8ecf">

## Zed
<img width="1722" alt="zed"
src="https://github.com/zed-industries/zed/assets/6967829/88436c78-93de-4e26-be15-b0dea6590c55">

crates/zed/src/languages.rs

@@ -10,6 +10,7 @@ use util::{asset_str, paths::PLUGINS_DIR};
 use self::{deno::DenoSettings, elixir::ElixirSettings};
 
 mod c;
+mod csharp;
 mod css;
 mod deno;
 mod elixir;
@@ -73,6 +74,11 @@ pub fn init(
         tree_sitter_cpp::language(),
         vec![Arc::new(c::CLspAdapter)],
     );
+    language(
+        "csharp",
+        tree_sitter_c_sharp::language(),
+        vec![Arc::new(csharp::OmniSharpAdapter {})],
+    );
     language(
         "css",
         tree_sitter_css::language(),