Refactor JerkTracker and MotionPredictor for better testing.

Changes include renaming forgetFactor to alpha.

Test: atest libinput_tests
Bug: 266747654
Bug: 353161308
Flag: com.android.input.flags.enable_prediction_pruning_via_jerk_thresholding
Change-Id: Icd056d36a3d7894c6c9b4b957233002ad961a9a1
diff --git a/include/input/TfLiteMotionPredictor.h b/include/input/TfLiteMotionPredictor.h
index 08a4330..49e909e 100644
--- a/include/input/TfLiteMotionPredictor.h
+++ b/include/input/TfLiteMotionPredictor.h
@@ -112,7 +112,7 @@
         float highJerk = 0;
 
         // Coefficient for the first-order IIR filter for jerk calculation.
-        float jerkForgetFactor = 1;
+        float jerkAlpha = 1;
     };
 
     // Creates a model from an encoded Flatbuffer model.