honor debugger frame selection in the frontend

[GitMensch]

For every command sent to GDB this extension does what it should do - it specifies the frame.

The part that is missing is to adjust the frame and thread active in the client in case of thread-selected events.
The most easy way to see it is by executing up/down and similar. GDB extensions also use these (often via python frame.select()) to explicit select something for the user.

I plan to tackle the selection, any insights how this is done would be nice, otherwise I'll check the docs.

[GitMensch]

Seems like there is no way back in the dap - so it would mean to do the necessary communication first.