[mdspan.layout.leftpad.obs, mdspan.layout.rightpad.obs] Fix return type of operator()

Author: hewillk

source/containers.tex

@@ -23723,7 +23723,7 @@
 
 \begin{itemdecl}
 template<class... Indices>
-constexpr size_t operator()(Indices... idxs) const noexcept;
+constexpr index_type operator()(Indices... idxs) const noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -24362,7 +24362,7 @@
 \indexlibrarymember{layout_right_padded::mapping}{operator()}%
 \begin{itemdecl}
 template<class... Indices>
-constexpr size_t operator()(Indices... idxs) const noexcept;
+constexpr index_type operator()(Indices... idxs) const noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}