Consider the screen still until proven otherwise

In order to avoid always forcing static mode after initialization or
recentering, consider the screen still by default.

This required adding a defaultValue option to the detector, to be used
during the initialization period.

Test: atest --host libheadtracking-test
Change-Id: I7f5a39a0fbca898c55f637e311ec1ea44a10d9f3
diff --git a/media/libheadtracking/HeadTrackingProcessor.cpp b/media/libheadtracking/HeadTrackingProcessor.cpp
index 257ee42..b2d2dbd 100644
--- a/media/libheadtracking/HeadTrackingProcessor.cpp
+++ b/media/libheadtracking/HeadTrackingProcessor.cpp
@@ -42,11 +42,13 @@
                   .rotationalDriftTimeConstant = options.rotationalDriftTimeConstant,
           }),
           mHeadStillnessDetector(StillnessDetector::Options{
+                  .defaultValue = false,
                   .windowDuration = options.autoRecenterWindowDuration,
                   .translationalThreshold = options.autoRecenterTranslationalThreshold,
                   .rotationalThreshold = options.autoRecenterRotationalThreshold,
           }),
           mScreenStillnessDetector(StillnessDetector::Options{
+                  .defaultValue = true,
                   .windowDuration = options.screenStillnessWindowDuration,
                   .translationalThreshold = options.screenStillnessTranslationalThreshold,
                   .rotationalThreshold = options.screenStillnessRotationalThreshold,