[libc++][NFC] Granularize <filesystem>

Granularize the `<filesystem>` header

Reviewed By: Quuxplusone, ldionne, #libc

Spies: libcxx-commits, mgorny

Differential Revision: https://reviews.llvm.org/D115578

NOKEYCHECK=True
GitOrigin-RevId: 7056250f517a9af0e26c019180c88a4bb5e691db
diff --git a/include/module.modulemap b/include/module.modulemap
index fa4170b..4194a7f 100644
--- a/include/module.modulemap
+++ b/include/module.modulemap
@@ -450,6 +450,25 @@
   module filesystem {
     header "filesystem"
     export *
+
+    module __filesystem {
+      module copy_options                 { private header "__filesystem/copy_options.h" }
+      module directory_entry              { private header "__filesystem/directory_entry.h" }
+      module directory_iterator           { private header "__filesystem/directory_iterator.h" }
+      module directory_options            { private header "__filesystem/directory_options.h" }
+      module file_status                  { private header "__filesystem/file_status.h" }
+      module file_time_type               { private header "__filesystem/file_time_type.h" }
+      module file_type                    { private header "__filesystem/file_type.h" }
+      module filesystem_error             { private header "__filesystem/filesystem_error.h" }
+      module operations                   { private header "__filesystem/operations.h" }
+      module path_iterator                { private header "__filesystem/path_iterator.h" }
+      module path                         { private header "__filesystem/path.h" }
+      module perm_options                 { private header "__filesystem/perm_options.h" }
+      module perms                        { private header "__filesystem/perms.h" }
+      module recursive_directory_iterator { private header "__filesystem/recursive_directory_iterator.h" }
+      module space_info                   { private header "__filesystem/space_info.h" }
+      module u8path                       { private header "__filesystem/u8path.h" }
+    }
   }
   module format {
     header "format"