Add PVS editor

[burninrubber0]

Adds a PVS editor with (more or less) full functionality. The previous editor was, in reality, a bare-bones viewer. This viewer has remained largely the same barring some fixes, minor additions, and input changes, with the editor being built around it.

Usage of the editor is intended to be intuitive. The controls are as follows:

• Click and drag to move
• Scroll to zoom
• Double click to select a zone
• R to reset position and zoom

Zones may also be selected from the zone list in the right-side panel. All editing takes place in this panel; the viewer will update in real time when changes are made. Upon selecting a zone, it will be highlighted in red and its neighbours will be highlighted in yellow. A zone's points may be edited by changing their X/Y values. Neighbours and their flags may be edited after being selected from the neighbour list. Zones and neighbours may be added or removed using their respective "Add" and "Delete" buttons.

For simplicity's sake, only features used in the retail game are present. This leads to the following divergences from the full PVS feature set:

• All zones must have 4 points. Zones deviating from this will likely break the editor.
  • Due to this, per-zone point start indices and per-zone point counts are ignored.
  • Also due to this, points not within zones are ignored.
• Only unsafe neighbours are read. Safe neighbours will be dropped if present.
• Zone types are ignored.
• Zone flags are ignored.

Again, these have no impact in practice as they are unused features in the retail game.

Also note:

• Any zone using a deleted zone as a neighbour will retain the relevant neighbour(s) only while the editor is open. After closing, deleted zones will be permanently removed from the neighbour array.
• Deletion of multiple zones or neighbours at once is unsupported. This feature may be added in the future.
• The original PC game is supported in addition to Remastered, but some aspects of the viewer (such as the map position) may be inaccurate.