Enable JLink in JTAG instead of SWD mode for debugging

[maxgerhardt]

The code at

platform-teensy/platform.py

Lines 74 to 83 in 586031e

	debug['tools']['jlink'] = {
	"server": {
	"package": "tool-jlink",
	"arguments": [
	"-singlerun",
	"-if", "SWD",
	"-select", "USB",
	"-device", debug.get("jlink_device"),
	"-port", "2331"
	],

Configures the debug_tool = jlink debugging method to hardcode SWD as the debugging protocol. There is no way to specify jtag here instead of swd normally, a user would have to specify a custom debug_server and friends command (which was e.g. done in this community post).

Interestingly, for uploading, such option is respected

platform-teensy/builder/main.py

Lines 189 to 195 in 586031e

	UPLOADERFLAGS=[
	"-device", board_config.get("debug", {}).get("jlink_device"),
	"-speed", "4000",
	"-if", ("jtag" if upload_protocol == "jlink-jtag" else "swd"),
	"-autoconnect", "1",
	"-NoGui", "1"
	],

And it then does a -if jtag.

Can the code be adapted so that if a user e.g. writes debug_tool = jlink-jtag, that change is also carried over?

The documentation at https://docs.platformio.org/en/latest/plus/debug-tools/jlink.html should be adapted accordingly then.