Windows companion build

[raphaelcoeffic]

This PR is aimed at compiling Companion for Windows with Github Actions.

This new system uses:

• MSYS2
• GCC 10.3
• Qt 5.12.9 (from aqtinstall)

It is noteworthy that the compatibility with MSVC was/is broken. For my part, I won't share a single tear 😇

Please note that #561 is based on this PR as well.

[elecpower]

Just in case you hadn't noticed ie buried in errors, build using Qt 5.15 libraries and thus depreciated warnings. The docker build and hence my dev and testing uses 5.11.

[elecpower]

PR #446 that will remove some of the depreciation warnings and compatible with 5.11

[elecpower]

A quick and dirty rename of the RGB define to say CPN_RBG is fine by me as it will not be needed in the next iteration of the colorlcd code that I'm working on.

[rotorman]

I tested this branch (wrote also instructions using it https://github.com/EdgeTX/edgetx/wiki/Build-Instructions-under-Windows-10-%28MSYS2%29 ), works nicely under Windows 10 64-bit.
I was able to build radio firmware for TX16S, Companion binary, Simulator binary, radio simulator library for TX16S and package the installer.

Only thing not working yet is the compact simu (make simu) under Windows 10 with MSYS2. Gives me:
make: *** No rule to make target 'simu'. Stop.

[rotorman]

Here some nice feedback to this PR and also to #555 / Companion from RCGroups:
https://www.rcgroups.com/forums/showthread.php?3916381-Official-EdgeTX-Version-2-4-0-Endeavour-Discussion-Thread/page45#post47804799

[raphaelcoeffic]

Superseded by #561