Remove viewport focus check from MapView _process

[Catylist0]

Summary

• Remove the per-frame viewport focus / is_input_handled() check from MapView._process that was clearing province hover.
• Track mouse presence over the map via NOTIFICATION_WM_MOUSE_ENTER and NOTIFICATION_WM_MOUSE_EXIT instead.

Made with Cursor

[wvpm]

From Devin:
_Missing window-focus-loss handling causes indefinite edge scrolling when alt-tabbing

The old code checked _is_viewport_inactive() every frame in _process, which returned true when not get_window().has_focus(). This set _mouse_over_viewport = false whenever the game window lost focus (e.g., alt-tab). The new code replaces this per-frame check with NOTIFICATION_WM_MOUSE_ENTER/NOTIFICATION_WM_MOUSE_EXIT notifications, but these only fire when the mouse cursor physically enters/leaves the window rect — they do not fire when the window merely loses focus while the cursor remains inside it.

Consequently, if the user alt-tabs away while the mouse cursor is near a window edge, _mouse_over_viewport stays true and _mouse_pos_viewport freezes at the last known position. Since _process continues running, edge_scrolling_vector() (MapView.gd:316-323) returns a non-zero vector every frame, causing the camera to scroll indefinitely until the user returns to the game.

To be fair, that is what Paradox games also do, so I suppose you nailed it.