Request a UI redraw on Drop of an Injector

This fixes the changed files picker when used against a clean worktree
for example. Without it the running indicator does not disappear. It
also simplifies the dynamic query handler's implementation so that it
doesn't need to request a redraw explicitly.

Co-authored-by: Pascal Kuthe <pascalkuthe@pm.me>

helix-event/src/lib.rs

@@ -34,7 +34,9 @@
 use anyhow::Result;
 pub use cancel::{cancelable_future, cancelation, CancelRx, CancelTx};
 pub use debounce::{send_blocking, AsyncHook};
-pub use redraw::{lock_frame, redraw_requested, request_redraw, start_frame, RenderLockGuard};
+pub use redraw::{
+    lock_frame, redraw_requested, request_redraw, start_frame, RenderLockGuard, RequestRedrawOnDrop,
+};
 pub use registry::Event;
 
 mod cancel;

helix-event/src/redraw.rs

@@ -51,3 +51,12 @@ pub fn start_frame() {
 pub fn lock_frame() -> RenderLockGuard {
     RENDER_LOCK.read()
 }
+
+/// A zero sized type that requests a redraw via [request_redraw] when the type [Drop]s.
+pub struct RequestRedrawOnDrop;
+
+impl Drop for RequestRedrawOnDrop {
+    fn drop(&mut self) {
+        request_redraw();
+    }
+}