Support selection of built-in decoders

[Entropy512]

Current Situation

Currently, this project builds in all decoders unless MY_DEVICES is set - in which case only a single decoder that is hardcoded is selected.

This leads to inefficiencies for the case where MY_DEVICES is not set, or having to manually change the hardcoded decoder when it is set

Proposed Change

Allow users to select built-in decoders using a build-time define

Additional Context

No response

[NorthernMan54]

I had tried unsuccessfully to find a way to do that easily with complier directives when doing the original development work. As the code needs a count of the number of devices to include. Do you have some thoughts on how to achieve that ?

[Entropy512]

Yeah, as I was digging through, it looks like doing it directly with compiler directives won't work, however this might:

https://docs.platformio.org/en/latest//manifests/library-json/fields/build/extrascript.html

If I'm reading that correctly, it looks like you could effectively run a variation of your rtl_433 import/update script automatically at build time to generate the DECLs in rtl_433_devices.h and signalDecoder.cpp - Probably don't want to touch those files directly, but you could probably create header fragments that are #included at the appropriate location within each file.

Not sure how to handle the OOK vs FSK stuff in signalDecoder without tracking that in a different location than currently that is easier to read from a Python script, although technically someone shouldn't be including both OOK and FSK devices when doing this to begin with. I only did it in my mangling of the devices specified by MY_DEVICES to support laziness when switching between FSK fineoffset and OOK neptune_r900.

[NorthernMan54]

If you want to submit a pull request, we can look at it.