Add support for detecting tests in source files, and implement it for Rust (#11195)

Continuing work from #10873 

Release Notes:

- N/A

---------

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/languages/src/rust.rs

@@ -389,6 +389,7 @@ impl ContextProvider for RustContextProvider {
                     "--".into(),
                     "--nocapture".into(),
                 ],
+                tags: vec!["rust-test".to_owned()],
                 ..TaskTemplate::default()
             },
             TaskTemplate {

crates/languages/src/rust/runnables.scm

@@ -0,0 +1,7 @@
+(
+    (attribute_item (attribute) @_attribute
+        (#match? @_attribute ".*test.*"))
+    .
+    (function_item
+        name: (_) @run)
+) @rust-test