PR #1968: Use std::move_backward within InlinedVector's Storage::Insert

Imported from GitHub PR https://github.com/abseil/abseil-cpp/pull/1968

Both libc++ and libstdc++ have optimizations within `std::move_backward` that support lowering to `memmove` when it is appropriate for the types involved. Using it significantly speeds up insert on vectors of trivial types such as integers.

This completely addresses the [poor insert performance relative to other inline capacity vectors](https://github.com/martinus/svector#random-insert) that others have observed. See also https://github.com/abseil/abseil-cpp/discussions/1934.
Merge 8ce6a5e699407321d2d229ca359f255463b05285 into 7374f9b0f4275df2e939f1aacbd323ad0182b897

Merging this change closes #1968

COPYBARA_INTEGRATE_REVIEW=https://github.com/abseil/abseil-cpp/pull/1968 from bdash:inlinedvector-insert-move 8ce6a5e699407321d2d229ca359f255463b05285
PiperOrigin-RevId: 828597732
Change-Id: Ica73f189f3fd5385ee90b532964ddf476d3fa223

absl/container/internal/inlined_vector.h

diff --git a/absl/container/internal/inlined_vector.h b/absl/container/internal/inlined_vector.h
index 85e8960..c7b709f 100644
--- a/absl/container/internal/inlined_vector.h
+++ b/absl/container/internal/inlined_vector.h
@@ -795,16 +795,9 @@
                                    move_construction_values,
                                    move_construction.size());
 
-    for (Pointer<A>
-             destination = move_assignment.data() + move_assignment.size(),
-             last_destination = move_assignment.data(),
-             source = move_assignment_values + move_assignment.size();
-         ;) {
-      --destination;
-      --source;
-      if (destination < last_destination) break;
-      *destination = std::move(*source);
-    }
+    std::move_backward(move_assignment_values,
+                       move_assignment_values + move_assignment.size(),
+                       move_assignment.data() + move_assignment.size());
 
     AssignElements<A>(insert_assignment.data(), values,
                       insert_assignment.size());