Fixes#1803
Running a command that created a new screen would previously result in a screen
order that looked like this, due to how `Screen::Hide` works:
- DF screen
- `command-prompt` screen (dismissed)
- New screen
The `command-prompt` screen remained on the stack until the new screen was
dismissed, so it would intercept viewscreen vmethod calls intended for the
DF screen.
This change adds a new behavior to `Screen::Hide` that results in this screen
order after running a command:
- DF screen
- New screen
- `command-prompt` screen (dismissed) - DF removes this screen immediately
command-prompt viewscreen may affect command execution if they are
looking for UI state. To make commands execute simillary to hotkeys or
console commands the viewscreen needs to removed from the top position.
Fixes#1194
The Screen::show takes ownership of the screen pointer. I decided to
switch the parameter to std::unique_ptr to make the pointer ownership
explicit. The unique_ptr then provides automatic screen destruction in
Screen::show unless pointer is inserted or is already in the linked list
that is managed by df.
This requires plugins to pass plugin_self to Screen::show(), but
avoids the need to implement special checks in plugin_onstatechange
for the SC_BEGIN_UNLOAD event.