[Contextual Edu] Added methods in aidl for updating edu data

- Added new method updateContextualEduStats in ISystemUiProxy.aidl for Launcher to update edu data.
- In EdgeBackGestureHandler, only updateContextualEduStats when mBackAnimation.onThresholdCrossed() is called, to ensure the action is a back swipe. In previous code, a swiping up to go home would also trigger calling updateContextualEduStats in EdgeBackGestureHandler which is incorrect.

Test: Manual
Bug: 357542123
Flag: com.android.systemui.keyboard_touchpad_contextual_education
Change-Id: I465593ad83ef44d1a399c9e82dfcb448f62439cc