ArduPlane: add climb before turn to AUTOLAND

[Hwurzburg]

Alternate to #29135

After test flying using a TX GCS to change climb to altitudes, I agree with Tim that this is easier to use then options in #29135...and it actually uses less flash so I am closing #29135

Now fully terrain following capable

[timtuxworth]

I think that's it just _m on values in meters.

[IamPete1]

Could we reuse RTL_CLIMB_MIN?

[Hwurzburg]

@tridge need help in getting glide_slope from point of climb to alt -> base loiter point to follow terrain...it always just use above home alt as it proceeds to the loiter-to-alt point....help would be appreciated

[Hwurzburg]

@tridge got it all working now.....full terrain support

[timtuxworth]

It seems to me that just because TERRAIN_ENABLE is true might not mean you want to use it for AUTOLAND. I guess it could be added to the TERRAIN_FOLLOW bitmask in a follow up PR.

[tridge]

i'm surprised you didn't need to subtract home alt here, I will need to look at this under gdb

[Hwurzburg]

set_target_altitude_location takes care of all that...the relative_alt bit is cleared when we convert the land alt to ABSOLUTE for later use...
since only the terrain alt flag is set when terrain following is enabled,

ardupilot/ArduPlane/altitude.cpp

Line 236 in bac78b5

if (!loc.relative_alt) {

removes the home alt