Correctly deal with sensor rotation in AHRS

[dellaert]

Sensor displacement rotation was not handled correctly in the AHRS factors. I spent a day tracking it down and fixed it:

• Significantly cleaned up testAHRSFactor.cpp, now uses FactorTesting.h macros
• To try and debug, deprecated two methods in PreintegratedRotation with hard-to-understand Jacobians
• Instead, added a function object with sane Jacobians, and fixed bug in Jacobians (missing chain rule).
• End-result is still not exactly how I'd like it ("insane" Jacobian in biascorrectedDeltaRij) but fixes bug

Tested:

• add testPreintegratedRotation.cpp, all tests pass
• Added new end-to-end integration test in testAHRSFactor.cpp, inspired by testImuFactor.cpp
• added a test in testManifoldPreintegration.cpp to establish equivalence
• added tests on deprecated methods, work, but deleted them in commit 1ac286f

[dellaert]

@andre-michelin Please review and confirm these changes work in our code?

[dellaert]

Thanks @varunagrawal , I addressed two of your comments in my local repo but will wait for Andre's comments to push, so we have to do CI only once more before merging.