Allow multiple input device in the same window

With this change, all restrictions about only having a single input
device active in a window are lifted.

The window will get multiple input devices at once.

21 native tests were forked in this CL to reflect the new behaviour.

Bug: 211379801
Test: navigate settings with touch + stylus at the same time
Test: swipe inside IME with touch + stylus
Test: draw in test app with touch + stylus
Test: TEST=inputflinger_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Change-Id: I259c0c87e47a1fa3090cddba6a595cf032877bb2
diff --git a/libs/input/input_flags.aconfig b/libs/input/input_flags.aconfig
index e041c51..e161c2a 100644
--- a/libs/input/input_flags.aconfig
+++ b/libs/input/input_flags.aconfig
@@ -137,3 +137,10 @@
   is_fixed_read_only: true
 
 }
+
+flag {
+  name: "enable_multi_device_same_window_stream"
+  namespace: "input"
+  description: "Allow multiple input devices to be active in the same window simultaneously"
+  bug: "330752824"
+}