[libc++] Implement `std::expected` P0323R12

Implement `std::expected` https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p0323r12.html

Added tests

Differential Revision: https://reviews.llvm.org/D124516

address comment

NOKEYCHECK=True
GitOrigin-RevId: e356f681f6c46ac35f933dc0cef3b25ceee8b210
diff --git a/include/module.modulemap.in b/include/module.modulemap.in
index 4033d2f..e6481a8 100644
--- a/include/module.modulemap.in
+++ b/include/module.modulemap.in
@@ -785,6 +785,17 @@
     header "execution"
     export *
   }
+  module expected {
+    header "expected"
+    export *
+
+    module __expected {
+      module bad_expected_access          { private header "__expected/bad_expected_access.h" }
+      module expected                     { private header "__expected/expected.h" }
+      module unexpect                     { private header "__expected/unexpect.h" }
+      module unexpected                   { private header "__expected/unexpected.h" }
+    }
+  }
   module filesystem {
     @requires_LIBCXX_ENABLE_FILESYSTEM@
     header "filesystem"