Track caller on <usize as ToOffset>::to_offset (#24503)

To get useful logs when reporting bugs involving offsets out of range

Release Notes:

- N/A

crates/gpui/src/arena.rs

@@ -116,6 +116,7 @@ impl<T: ?Sized> ArenaBox<T> {
         }
     }
 
+    #[track_caller]
     fn validate(&self) {
         assert!(
             self.valid.get(),

crates/multi_buffer/src/multi_buffer.rs

@@ -7320,6 +7320,7 @@ impl ToOffset for Point {
 }
 
 impl ToOffset for usize {
+    #[track_caller]
     fn to_offset<'a>(&self, snapshot: &MultiBufferSnapshot) -> usize {
         assert!(*self <= snapshot.len(), "offset is out of range");
         *self