PositionControl: deconflict velocity control gains from thrust

[MaEtUgR]

Describe problem solved by this pull request
Before #14212 the velocity control gains used in the multicopter position controller were defined as a scale between velocity error in one axis (or it's integral and derivative respectively) and the unit thrust vector. The problem with this is that the normalization of the unit thrust vector changes per vehicle or even vehicle configuration as 0 and 100% thrust get a different physical response. That's why the gains are now defined as scale between velocity error (integral/derivative) and the output acceleration in m/s². E.g. with the default P horizontal velocity gain of 4 m/s² per m/s you would counteract a velocity error of 1m/s with 4m/s² actuation in order to accelerate to the desired velocity. This leads to less dependence of the velocity control tuning to the vehicles maximum thrust, output configuration and hover thrust.

In #14212 a backward compatibility factor was introduced to make the existing parameters backward compatible. This pull request aims at:

1. fixes Multicopter velocity control gains backwards compatibility depends on hover thrust #14720
2. Make the parameters reflect that reproducible gain scale while still staying backwards compatible.

Describe your solution

• Avoid constantly adjusting the velocity gains with the HTE
• Make sure the hover thrust integral update doesn't break
  even though its unit is acceleration and not unit thrust anymore
• Replace the existing parameters with new ones that directly reflect the correctly scaled values

In horizontal direction it doesn't make sense to scale them with the hover thrust and in vertical direction the adjustments are already done in the acceleration to collective thrust conversion.

Test data / coverage
SITL tested and real world tested, see #14749 (comment)

[MaEtUgR]

I went out real-world testing this pr and found the problem #14821 which was already present before and is not caused by this pr. The problem shows in the takeoff of the last three logs.

Here are the test logs for this pr:
stabilized, altitude: https://logs.px4.io/plot_app?log=153e83cb-60e4-408b-96cd-2336cc2b4432
stabilized, altitude, position: https://logs.px4.io/plot_app?log=b0fc3935-98fe-418e-bdae-8855066d569d
position: https://logs.px4.io/plot_app?log=219ac076-694d-4e85-8618-7665d62b349b
position 2: https://logs.px4.io/plot_app?log=b21d1d59-04c7-4d96-aaad-87a8401e69e2
position 3: https://logs.px4.io/plot_app?log=13f14b3b-d919-432c-9e89-f0610ec7285c

The pr works like expected. Please review the _ACC parameter name changes and transitioning code in the second commit. I noticed when switching to a new PX4 branch after this commit and to an older one again you lose the custom velocity control tuning e.g. SITL defaults. I'm also happy if we just merge the first commit if discussion about the parameters continues.

[MaEtUgR]

As proposed in the last comment I separated out the really important gain fix in this pr from the parameter rescaling #14823. That should make it far easier to review.