Add device reset

[thorstendb-ARM]

Adds:

Custom Reset (configured via launch.json).
Issue: #359

Testing:

Required: eclipse-cdt-cloud/cdt-gdb-vscode#152
In a target project, launch.json, add this. The command uses pyOCD but can be any other.

    "configurations": [
        {
            "name": "pyOCD cdt-gdb-adapter",
            ...
            "customResetCommands": [
                "monitor reset halt hardware",
            ],
        },

Note:

The GUI update depends on an asynchronous event from GDB (such as Target STOPPED), likely triggered by the connected target debugger. If this event is absent (e.g. in current pyOCD), test it by performing a single step-into after pressing the Custom Reset button.

[jreineckearm]

The functionality in the PR is complete. Still trying to make the automated tests work on our end before adding some for this PR.

[jreineckearm]

Nice, changes look good to me! And work nicely in combination with eclipse-cdt-cloud/cdt-gdb-vscode#152 .

Makes sense to only support for gdbtarget type while having parts of the implementation in the base classes for both.
It would in theory also work for gdb type. But I don't see the use case.
Button in GUI is correctly hidden if not using customResetCommands.

Good to merge as far as I am concerned. Merging only tomorrow (CET) though to give others the chance to review (CC: @asimgunes , @jonahgraham )

[jonahgraham]

Can the new code be de-duplicated? customResetCommands was added to GDBDebugSession but customResetRequest was added to GDBTargetDebugSession. That means customResetCommands is effectively unreferenced in GDBDebugSession.

Can you move all of it to GDBDebugSessionBase?