Debugger: Fix #11430.

InspectorWindow:
- Inherit from Team::Listener and implement hook for thread state
  change events.
- On thread state change, if the new state is stopped, and we have
  an active block, release it, and ask to re-inspect.
- Factor out helper function for updating the active block.
- Always ensure the MemoryView is updated when we change blocks.

MemoryView:
- Clean up acquisition of target memory block.

This ensures that the block data is kept up to date when stepping
through code with an inspector window open.