Inline absl::void_t to std::void_t wherever possible

This won't replace all call sites, but that's fine. We only want to replace the call sites that compile fine, since they don't need to use absl::void_t.

PiperOrigin-RevId: 896017307
Change-Id: I7e78066dc973e135922b11fba5c7642563ef6a67

absl/meta/type_traits.h

diff --git a/absl/meta/type_traits.h b/absl/meta/type_traits.h
index 9013aea..bcc3a98 100644
--- a/absl/meta/type_traits.h
+++ b/absl/meta/type_traits.h
@@ -104,11 +104,13 @@
 // metafunction allows you to create a general case that maps to `void` while
 // allowing specializations that map to specific types.
 //
-// This metafunction is not 100% compatible with the C++17 `std::void_t`
-// metafunction. It has slightly different behavior, such as when ordering
-// partial specializations. It is recommended to use `std::void_t` instead.
+// This metafunction is a workaround for some implementations of `std::void_t`
+// that evaluate to `void` prematurely, causing partial specializations to
+// appear duplicated (and thus invalid) to the compiler prior to substitution
+// taking place. Whenever possible, use `std::void_t` instead.
 template <typename... Ts>
-using void_t = typename type_traits_internal::VoidTImpl<Ts...>::type;
+using void_t ABSL_REFACTOR_INLINE =
+    typename type_traits_internal::VoidTImpl<Ts...>::type;
 
 // Historical note: Abseil once provided implementations of these type traits
 // for platforms that lacked full support. New code should prefer to use the