ekf2_main - Add optical flow innovation pre-flight check (#13036)

* ekf2: Add FirstOrderLpf and InnovationLpf classes for innovation lowpass filtering

* ekf2: use InnovLpf filter class in preflight checks

* ekf2: move selection of yaw test limit for pre-flight check in function

* ekf2: Move pre-flight checks into separate function

* ekf2: use static constexpr insetead of inline for sq (square) function

* ekf2: Split pre-flight checks in separate functions
Also use the same check for all the innovations:
innov_lpf < test and innov < 2xtest

* ekf2: Add optical flow pre-flight check

* ekf2: Combine FirstOrderLpf and InnovationLpf in single class

* ekf2: check vel_pos_innov when ev_pos is active as well

* ekf2: transform InnovationLpf into a header only library and pass the
spike limit during the update call to avoid storing it here

* ekf2: Static and const cleanup
- set spike_lim constants as static constexpr, set innovation
- set checker helper functions as static
- rename the mix of heading and yaw as heading to avoid confusion

* ekf2: use ternary operator in selectHeadingTestLimit instead of if-else

* ekf2: store intermediate redults in const bool flags. Those will be used for logging

* ekf2: set variable const whenever possible

* ekf2: create PreFlightChecker class that handle all the innovation
pre-flight checks.
Add simple unit testing
Use bitmask instead of general flag to have more granularity

* PreFlightChecker: use setter for the innovations to check instead of sending booleans in the update function
This makes it more scalable as more checks will be added

* ekf: Use booleans instead of bitmask for ekf preflt checks
Rename "down" to "vert"

src/modules/ekf2/CMakeLists.txt

@@ -30,6 +30,9 @@
 # POSSIBILITY OF SUCH DAMAGE.
 #
 #############################################################################
+
+add_subdirectory(Utility)
+
 px4_add_module(
 	MODULE modules__ekf2
 	MAIN ekf2
@@ -42,4 +45,5 @@ px4_add_module(
 		ecl_EKF
 		ecl_geo
 		perf
+		Ekf2Utility
 	)