[libc++] Support arrays in make_shared and allocate_shared (P0674R1)

This patch implements P0674R1, i.e. support for arrays in std::make_shared
and std::allocate_shared.

Co-authored-by: Zoe Carver <z.zoelec2@gmail.com>

Differential Revision: https://reviews.llvm.org/D62641

NOKEYCHECK=True
GitOrigin-RevId: e27a122b3abc5000e99239f3df6e6d4e32b7dc81
diff --git a/docs/FeatureTestMacroTable.rst b/docs/FeatureTestMacroTable.rst
index 8877ec0..e305a78 100644
--- a/docs/FeatureTestMacroTable.rst
+++ b/docs/FeatureTestMacroTable.rst
@@ -268,6 +268,8 @@
     ------------------------------------------------- -----------------
     ``__cpp_lib_semaphore``                           ``201907L``
     ------------------------------------------------- -----------------
+    ``__cpp_lib_shared_ptr_arrays``                   ``201707L``
+    ------------------------------------------------- -----------------
     ``__cpp_lib_shift``                               ``201806L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_smart_ptr_for_overwrite``             *unimplemented*
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index ea42b56..dc86c58 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -42,6 +42,8 @@
 
 - Implemented P1165R1 (Make stateful allocator propagation more consistent for ``operator+(basic_string)``)
 
+- Implemented P0674R1 (Support arrays in make_shared and allocate_shared)
+
 - `pop_heap` now uses an algorithm known as "bottom-up heapsort" or
   "heapsort with bounce" to reduce the number of comparisons, and rearranges
   elements using move-assignment instead of `swap`.
diff --git a/docs/Status/Cxx20Papers.csv b/docs/Status/Cxx20Papers.csv
index 438e1f0..de07254 100644
--- a/docs/Status/Cxx20Papers.csv
+++ b/docs/Status/Cxx20Papers.csv
@@ -1,6 +1,6 @@
 "Paper #","Group","Paper Name","Meeting","Status","First released version"
 "`P0463R1 <https://wg21.link/P0463R1>`__","LWG","Endian just Endian","Toronto","|Complete|","7.0"
-"`P0674R1 <https://wg21.link/P0674R1>`__","LWG","Extending make_shared to Support Arrays","Toronto","",""
+"`P0674R1 <https://wg21.link/P0674R1>`__","LWG","Extending make_shared to Support Arrays","Toronto","|Complete|","15.0"
 "","","","","",""
 "`P0020R6 <https://wg21.link/P0020R6>`__","LWG","Floating Point Atomic","Albuquerque","",""
 "`P0053R7 <https://wg21.link/P0053R7>`__","LWG","C++ Synchronized Buffered Ostream","Albuquerque","",""