Send_position_target_global_int: Set mavlink altitude frame to be target's frame

[hendjoshsr71]

This changes the send_position_target_global_int message to send the target's altitude mavlink frame in the same frame as the target's location frame.

Example: below uses waypoints in terrain, ASML, and above home frames.
Note this currently ends up being filled by AC_WP_Nav::get_wp_nav() which always sets the target to terrain or ASML. To get the above home frame filled in would require a bit work since that is not used in WP_Nav.

Master

After PR

[rmackay9]

I think this is probably most useful in Guided mode where the caller may want to check that what they've sent in has been consumed correctly.

[hendjoshsr71]

EDIT: moving all the below to separate PRs.
- Based on a request in discord, added send_position_target_global_int to Sub
- moved the message to gcs_common
- TODO: add the autotests

ArduSub receiving the message

[hendjoshsr71]

Updated this so that the commanded altitude frames for guided and auto modes can also report relative to home in addition to terrain & absolute frames.

Rover Autotest may fail: I think this is due to the issue with terrain in CI as it passes locally. There is an argument to be made that there isn't a lot of purpose to testing rover for differing altitude frames since it ignores altitude.

[hendjoshsr71]

I've disabled the terrain frame autotest for now in this PR after fixing the altitude frame conversion in autotest. See this issue for why #18788

Mission Below: Sets Relative Frame 50m then 100m then 50m, Terrain 100m then 150m then 100m, then Absolute Frame 1200m then 1250m

Master: Red Position_Target.Altitude

After PR: Green Position_Target.Altitude

[hendjoshsr71]

@peterbarker Any thoughts on disabling set_position_target_zzz terrain frame testing as I do in this PR because of issue #18788 ? Or on my autotest changes here?