fix: Ext module not powered when using SBUS or CPPM trainer

[bug400]

Fixes #3634, fixes #2009

Summary of changes:
Power on/off of the external module is now in the module init/deinit code. Since trainer/sbus and trainer/ccpm are no modules, power on/off is not handled for that mode of operation. Therefore, moduleSetPower calls were added to the init/deinit subroutines for trainer/sbus and trainer/cppm. There is also a fix in stop_trainer_module_sbus() where sbus_trainer_mod_st has to be set to nullptr after deiniztialization of the sbus port.

Tested on QX7-ACCESS with edgetx 2.9.1 with mode trainer/sbus (with SBUS data source and power pin voltage check) and with mode trainer/sbus (power pin voltage check only, I do not have a ccpm data source).

[pfeerick]

This should have been targeted against the main branch, but will be messy to change, so can be cherry-picked into main afterwards.

[raphaelcoeffic]

This should have been targeted against the main branch, but will be messy to change, so can be cherry-picked into main afterwards.

I force-pushed the cherry-picked code now based on main onto his branch ;-)

[BergWolfRC]

Thanks for providing this fix.
On my TX1S MKII with EdgeTX 2.9.1 I encountered specifically the problem that the external module was not powered when using CPPM trainer.
Now, with EdgeTX 2.9.4 installed I do get the power for the external module in this case.
However the PPM signal of the receiver connected to the external module bay (PPM via Pin 2) is not recognized by the TX even if trainer special function is enabled (set to sticks). Could this be another side effect of the changes in the code?
I am using a cm410X as receiver in the trainer tx for receiving the student signals (servo attached to the RX does move).

[mha1]

I can confirm this, see #4672

[BergWolfRC]

thanks for double checking, confirming and creating the follow up issue!
You guys rock!