editor: Move runnables querying to background thread (#11487)

Originally reported by @mrnugget and @bennetbo 
Also, instead of requerying them every frame, we do so whenever buffer
changes.

As a bonus, I modified tree-sitter query for Rust tests.

Release Notes:

- N/A

crates/languages/src/rust/runnables.scm

@@ -1,6 +1,6 @@
 (
     (attribute_item (attribute) @_attribute
-        (#match? @_attribute ".*test.*"))
+        (#match? @_attribute ".*test"))
     .
     (function_item
         name: (_) @run)