Fixes for C++20 support.

Various things are deprecated or removed in C++20, including
* Various allocator member types
* std::iterator
* std::result_of

Replace these with supported versions.

Bug: chromium:1284275
Change-Id: I11a2909e3a269cdb98ada2bd6621086409878242
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/89040
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Auto-Submit: Peter Kasting <pkasting@google.com>
Commit-Queue: Peter Kasting <pkasting@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>

src/dawn/common/StackContainer.h

@@ -34,8 +34,8 @@
 template <typename T, size_t stack_capacity>
 class StackAllocator : public std::allocator<T> {
   public:
-    typedef typename std::allocator<T>::pointer pointer;
-    typedef typename std::allocator<T>::size_type size_type;
+    typedef typename std::allocator_traits<std::allocator<T>>::pointer pointer;
+    typedef typename std::allocator_traits<std::allocator<T>>::size_type size_type;
 
     // Backing store for the allocator. The container owner is responsible for
     // maintaining this for as long as any containers using this allocator are

src/dawn/tests/ParamGenerator.h

@@ -53,8 +53,14 @@ class ParamGenerator {
         }
     }
 
-    class Iterator : public std::iterator<std::forward_iterator_tag, ParamStruct, size_t> {
+    class Iterator {
       public:
+        using iterator_category = std::forward_iterator_tag;
+        using value_type = ParamStruct;
+        using difference_type = size_t;
+        using pointer = ParamStruct*;
+        using reference = ParamStruct&;
+
         Iterator& operator++() {
             // Increment the Index by 1. If the i'th place reaches the maximum,
             // reset it to 0 and continue with the i+1'th place.

src/tint/clone_context.h

@@ -17,6 +17,7 @@
 
 #include <algorithm>
 #include <functional>
+#include <type_traits>
 #include <unordered_map>
 #include <unordered_set>
 #include <utility>
@@ -366,7 +367,7 @@ class CloneContext {
     /// references of the original object. A type mismatch will result in an
     /// assertion in debug builds, and undefined behavior in release builds.
     /// @returns this CloneContext so calls can be chained
-    template <typename WHAT, typename WITH, typename = std::result_of_t<WITH()>>
+    template <typename WHAT, typename WITH, typename = std::invoke_result_t<WITH>>
     CloneContext& Replace(const WHAT* what, WITH&& with) {
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, what);
         replacements_[what] = with;