device: Replace query_count parameter in get_query_pool_results with data.len() (#644)

A slice is designed to be a cheap view into a continuous segment of
memory and easily recreated with a different offset and size.  This can
be used to our advantage to let the user set exactly how many items they
want to request, while ensuring all returned slots are filled on success
or otherwise return `NOT_READY` if not enough query results could be
copied to user memory (or block if the `WAIT` flag is set).

This also opens the door to accepting `MaybeUninit` in the future and
returning the initialized slice in the `VkResult::Ok(here)` case.

ash/src/device.rs

@@ -2016,21 +2016,15 @@ impl Device {
         &self,
         query_pool: vk::QueryPool,
         first_query: u32,
-        query_count: u32,
         data: &mut [T],
         flags: vk::QueryResultFlags,
     ) -> VkResult<()> {
-        let data_length = query_count as usize;
-        assert!(
-            data_length <= data.len(),
-            "query_count was higher than the length of the slice"
-        );
-        let data_size = mem::size_of::<T>() * data_length;
+        let data_size = mem::size_of_val(data);
         (self.device_fn_1_0.get_query_pool_results)(
             self.handle(),
             query_pool,
             first_query,
-            query_count,
+            data.len() as u32,
             data_size,
             data.as_mut_ptr() as *mut _,
             mem::size_of::<T>() as _,