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/csharp.rs

@@ -0,0 +1,144 @@
+use anyhow::{anyhow, Context, Result};
+use async_compression::futures::bufread::GzipDecoder;
+use async_tar::Archive;
+use async_trait::async_trait;
+use futures::{io::BufReader, StreamExt};
+use language::{LanguageServerName, LspAdapterDelegate};
+use lsp::LanguageServerBinary;
+use smol::fs;
+use std::env::consts::ARCH;
+use std::ffi::OsString;
+use std::{any::Any, path::PathBuf};
+use util::async_maybe;
+use util::github::latest_github_release;
+use util::{github::GitHubLspBinaryVersion, ResultExt};
+
+pub struct OmniSharpAdapter;
+
+#[async_trait]
+impl super::LspAdapter for OmniSharpAdapter {
+    fn name(&self) -> LanguageServerName {
+        LanguageServerName("OmniSharp".into())
+    }
+
+    fn short_name(&self) -> &'static str {
+        "OmniSharp"
+    }
+
+    async fn fetch_latest_server_version(
+        &self,
+        delegate: &dyn LspAdapterDelegate,
+    ) -> Result<Box<dyn 'static + Send + Any>> {
+        let release =
+            latest_github_release("OmniSharp/omnisharp-roslyn", false, delegate.http_client())
+                .await?;
+
+        let mapped_arch = match ARCH {
+            "aarch64" => Some("arm64"),
+            "x86_64" => Some("x64"),
+            _ => None,
+        };
+
+        match mapped_arch {
+            None => Ok(Box::new(())),
+            Some(arch) => {
+                let asset_name = format!("omnisharp-osx-{}-net6.0.tar.gz", arch);
+                let asset = release
+                    .assets
+                    .iter()
+                    .find(|asset| asset.name == asset_name)
+                    .ok_or_else(|| anyhow!("no asset found matching {:?}", asset_name))?;
+                let version = GitHubLspBinaryVersion {
+                    name: release.name,
+                    url: asset.browser_download_url.clone(),
+                };
+
+                Ok(Box::new(version) as Box<_>)
+            }
+        }
+    }
+
+    async fn fetch_server_binary(
+        &self,
+        version: Box<dyn 'static + Send + Any>,
+        container_dir: PathBuf,
+        delegate: &dyn LspAdapterDelegate,
+    ) -> Result<LanguageServerBinary> {
+        let version = version.downcast::<GitHubLspBinaryVersion>().unwrap();
+        let binary_path = container_dir.join("omnisharp");
+
+        if fs::metadata(&binary_path).await.is_err() {
+            let mut response = delegate
+                .http_client()
+                .get(&version.url, Default::default(), true)
+                .await
+                .context("error downloading release")?;
+            let decompressed_bytes = GzipDecoder::new(BufReader::new(response.body_mut()));
+            let archive = Archive::new(decompressed_bytes);
+            archive.unpack(container_dir).await?;
+        }
+
+        fs::set_permissions(
+            &binary_path,
+            <fs::Permissions as fs::unix::PermissionsExt>::from_mode(0o755),
+        )
+        .await?;
+        Ok(LanguageServerBinary {
+            path: binary_path,
+            arguments: server_binary_arguments(),
+        })
+    }
+
+    async fn cached_server_binary(
+        &self,
+        container_dir: PathBuf,
+        _: &dyn LspAdapterDelegate,
+    ) -> Option<LanguageServerBinary> {
+        get_cached_server_binary(container_dir).await
+    }
+
+    async fn installation_test_binary(
+        &self,
+        container_dir: PathBuf,
+    ) -> Option<LanguageServerBinary> {
+        get_cached_server_binary(container_dir)
+            .await
+            .map(|mut binary| {
+                binary.arguments = vec!["--help".into()];
+                binary
+            })
+    }
+}
+
+async fn get_cached_server_binary(container_dir: PathBuf) -> Option<LanguageServerBinary> {
+    async_maybe!({
+        let mut last_binary_path = None;
+        let mut entries = fs::read_dir(&container_dir).await?;
+        while let Some(entry) = entries.next().await {
+            let entry = entry?;
+            if entry.file_type().await?.is_file()
+                && entry
+                    .file_name()
+                    .to_str()
+                    .map_or(false, |name| name == "omnisharp")
+            {
+                last_binary_path = Some(entry.path());
+            }
+        }
+
+        if let Some(path) = last_binary_path {
+            Ok(LanguageServerBinary {
+                path,
+                arguments: server_binary_arguments(),
+            })
+        } else {
+            Err(anyhow!("no cached binary"))
+        }
+    })
+    .await
+    .log_err()
+}
+
+fn server_binary_arguments() -> Vec<OsString> {
+    vec!["-lsp".into()]
+}