DeviceConfig: Split android:window_manager into android and window_manager

The keys are split according to whether they affect the system as a whole,
or simply the inner workings of the window manager.

Also encapsulates WindowManagerConstants properly and adds testing.

Bug: 139735771
Test: atest WindowManagerConstantsTest
Change-Id: I67c96a2bdd3140fe2ff9c6832d2d69f2e57115e2
diff --git a/services/tests/wmtests/src/com/android/server/wm/DisplayContentTests.java b/services/tests/wmtests/src/com/android/server/wm/DisplayContentTests.java
index 571f214..ac87de3 100644
--- a/services/tests/wmtests/src/com/android/server/wm/DisplayContentTests.java
+++ b/services/tests/wmtests/src/com/android/server/wm/DisplayContentTests.java
@@ -872,7 +872,7 @@
 
     @Test
     public void testCalculateSystemGestureExclusion_immersiveStickyLegacyWindow() throws Exception {
-        mWm.mSystemGestureExcludedByPreQStickyImmersive = true;
+        mWm.mConstants.mSystemGestureExcludedByPreQStickyImmersive = true;
 
         final DisplayContent dc = createNewDisplay();
         final WindowState win = createWindow(null, TYPE_BASE_APPLICATION, dc, "win");