Add support for left-right splits on portrait devices

- Add a config to transpose the split such that you can split left/right
  while in portrait.  This is mostly useful for portrait based foldable
  devices.
- Refactors the divider, split layout, and drag and drop to be based on
  this new config vs the configuration orientation

Bug: 291018646
Test: Manual
Flag: enable_left_right_split_in_portrait
Change-Id: I8b3b81f2510457c31ababb2db1b5e4031d6dc17c
diff --git a/libs/WindowManager/Shell/aconfig/multitasking.aconfig b/libs/WindowManager/Shell/aconfig/multitasking.aconfig
index 4d2d960..4511f3b 100644
--- a/libs/WindowManager/Shell/aconfig/multitasking.aconfig
+++ b/libs/WindowManager/Shell/aconfig/multitasking.aconfig
@@ -50,3 +50,10 @@
     bug: "290220798"
     is_fixed_read_only: true
 }
+
+flag {
+    name: "enable_left_right_split_in_portrait"
+    namespace: "multitasking"
+    description: "Enables left/right split in portrait"
+    bug: "291018646"
+}