feat(lsp): pass client_info on initialization (#4904)

Pass client name ('helix') and client version (version / git hash)
to LSP server on initialization.

helix-loader/build.rs

@@ -1,6 +1,26 @@
+use std::borrow::Cow;
+use std::process::Command;
+
+const VERSION: &str = include_str!("../VERSION");
+
 fn main() {
+    let git_hash = Command::new("git")
+        .args(["rev-parse", "HEAD"])
+        .output()
+        .ok()
+        .filter(|output| output.status.success())
+        .and_then(|x| String::from_utf8(x.stdout).ok());
+
+    let version: Cow<_> = match git_hash {
+        Some(git_hash) => format!("{} ({})", VERSION, &git_hash[..8]).into(),
+        None => VERSION.into(),
+    };
+
     println!(
         "cargo:rustc-env=BUILD_TARGET={}",
         std::env::var("TARGET").unwrap()
     );
+
+    println!("cargo:rerun-if-changed=../VERSION");
+    println!("cargo:rustc-env=VERSION_AND_GIT_HASH={}", version);
 }