Sticks : Add utility functions to get pitch, roll, throttle and yaw values more intuitively

[junwoo091400]

Describe problem solved by this pull request
'Sticks' utility library is used by Flight Tasks. While implementing a Follow-Target feature (#19260) with RC-controllable behavior, I found that it is unclear as to which 'user input' each input vector corresponds to.

Describe your solution
Added functions each returning user input values in a clear, intuitive naming.

• Also renamed the 'checkAndSetStickInputs' function name to 'checkAndUpdateStickInputs', since 'set' doesn't imply that the stick values are update, which is the most important aspect of this function, thus avoiding possible confusions ;)

[MaEtUgR]

I was planning to introduce such getters so I'm really much in favor. Can we quickly discuss the details?

[MaEtUgR]

The definition and order of the sticks comes from the global definition here:

PX4-Autopilot/msg/manual_control_setpoint.msg

Lines 25 to 43 in 4a5a8d5

	float32 x # stick position in x direction -1..1
	# in general corresponds to forward/back motion or pitch of vehicle,
	# in general a positive value means forward or negative pitch and
	# a negative value means backward or positive pitch
	float32 y # stick position in y direction -1..1
	# in general corresponds to right/left motion or roll of vehicle,
	# in general a positive value means right or positive roll and
	# a negative value means left or negative roll
	float32 z # throttle stick position 0..1
	# in general corresponds to up/down motion or thrust of vehicle,
	# in general the value corresponds to the demanded throttle by the user,
	# if the input is used for setting the setpoint of a vertical position
	# controller any value > 0.5 means up and any value < 0.5 means down
	float32 r # yaw stick/twist position, -1..1
	# in general corresponds to the righthand rotation around the vertical
	# (downwards) axis of the vehicle

How about referencing it here instead of only explaining roll, pitch, yaw and throttle?

[MaEtUgR]

Closely related my goal is to unify the stick definitions and make the description easier to read:
https://github.com/PX4/PX4-Autopilot/pull/15949/files#diff-cdbc310b47e9f8baaa9198133a1adc0cb4ae571a0ca91c2ef3df45db4a1e216dR16-R25

[MaEtUgR]

We just discussed and the conclusion was the only thing that should change for clarity is the name of getThrottle() to be very explicit that it's [-1, 1].