Add support for custom gdbHost in jlink servertype

[sigurdal]

This adds support for specifying the host for GDB when running with "servertype": "jlink".

This is to allow running the build environment and GDB runs in WSL, while having JLinkGDBServerCL run in Windows and thus avoiding mapping the USB device into WSL.

If not set, it defaults to localhost to maintain backwards compatibility.

In my setup I have the following lines in settings.json:

{
    "cortex-debug.JLinkGDBServerPath": "/mnt/c/Program Files/SEGGER/JLink/JLinkGDBServerCL.exe",
    "cortex-debug.gdbPath": "/path/to/bin/arm-none-eabi-gdb"
}

And add the following lines to launch.json:

"gdbHost": "172.X.Y.1",
"serverArgs": [
    "-nolocalhostonly",
],

But as the WSL IP might change, it can be automatically updated, for example by using the augustocdias.tasks-shell-input extension and:

"configurations": [
    {
        "name": "Debug with J-Link",
        "gdbHost": "${input:wslHostIp}",
        "serverArgs": [
            "-nolocalhostonly",
        ],
        ...
    }
],
"inputs": [
    {
        "id": "wslHostIp",
        "type": "command",
        "command": "shellCommand.execute",
        "args": {
            "command": "ip route show | grep -i default | awk '{ print $3}'",
            "cwd": "${workspaceFolder}",
            "useSingleResult": true
        },
    }
]