Handle debug session end

[dqna64]

Is your feature request related to a problem? Please describe.
When user finishes debugging their program...

Describe the solution you'd like

• Debugger BE kill gdb subprocess
• Debugger BE send "programFinish" event to FE
• FE indicate program finished, next button turns into "exit" button -- clear type annotations, stack inspector, console

Describe alternatives you've considered
Right now BE keep GDB process running and keeps calling custom_next command even tho program finished in gdb
Right now FE keeps allowing user to trigger executeNext events to debugger BE

Additional context