Add runnable for rust main function (#13087)

Release Notes:

- N/A



https://github.com/zed-industries/zed/assets/21101490/7a57805c-1d31-48b2-bc2c-3a6f0b730d72

crates/languages/src/rust/runnables.scm

@@ -25,3 +25,15 @@
     )
     (#set! tag rust-test)
 )
+
+; Rust main function
+(
+    (
+        (function_item
+            name: (_) @run
+            body: _
+        ) @_rust_main_function_end
+        (#eq? @run "main")
+    )
+    (#set! tag rust-main)
+)