Add unit tests for DataValidator

[tstellanova]

Added a few unit tests for the DataValidator class that cover happy path and common failure paths. In some cases the existing interface lacks documentation of expected behavior (for example DataValidator::confidence has some undocumented side-effects, setting _error_mask, and put performs a variety of calculations), so these tests codify some of the "as-built" behavior of the class. I did not yet attempt to test the vibration-calculating code, which is unspecified but appears to be key to the operation of DataValidatorGroup.

[dagar]

Looks like a good start.

Not that we've defined this anywhere, but would you mind running it through PX4's astyle?
From Firmware ./Tools/astyle/fix_code_style.sh validation/tests/*.cpp.

[priseborough]

These changes appear to be causing a problem with PX4/Firmware CI testing.

http://ci.px4.io:8080/blue/organizations/jenkins/PX4_misc%2FFirmware-compile_mac/detail/PR-11630/2/pipeline

[tstellanova]

It looks like they are passing in this CI:
https://codecov.io/gh/PX4/ecl/src/master/validation/tests/test_data_validator.cpp
I'm not familiar with the other CI. @dagar Any recommendations on how to ensure this test binary builds in that CI ?

[tstellanova]

My initial thought is that it appears the ci.px4.io CI build is treating the ecl_test_data_validator binary as one of the sitl unit tests, similar to eg autodeclination. Not sure why it's deciding to do that.

[dagar]

I'll limit the ecl tests to the standalone build. #591