Add stride accessor for Vec

Will be required for implementing an iterator.
diff --git a/macro/src/expand.rs b/macro/src/expand.rs
index 15351f0..7503f3a 100644
--- a/macro/src/expand.rs
+++ b/macro/src/expand.rs
@@ -541,11 +541,13 @@
     let link_drop = format!("{}drop", link_prefix);
     let link_len = format!("{}len", link_prefix);
     let link_data = format!("{}data", link_prefix);
+    let link_stride = format!("{}stride", link_prefix);
 
     let local_prefix = format_ident!("{}__vec_", ident);
     let local_drop = format_ident!("{}drop", local_prefix);
     let local_len = format_ident!("{}len", local_prefix);
     let local_data = format_ident!("{}data", local_prefix);
+    let local_stride = format_ident!("{}stride", local_prefix);
 
     let span = ty.span();
     quote_spanned! {span=>
@@ -564,6 +566,11 @@
         unsafe extern "C" fn #local_data(this: *const ::cxx::private::RustVec<#inner>) -> *const #inner {
             (*this).as_ptr()
         }
+        #[doc(hidden)]
+        #[export_name = #link_stride]
+        unsafe extern "C" fn #local_stride() -> usize {
+            ::std::mem::size_of::<#inner>()
+        }
     }
 }