Simplify the usage of datafile reader and writer by adding utility functions to read and write zero-terminated UTF-8 strings.
Improve validation of string data read from datafiles. It is ensure that string data is null-terminated, has no internal NUL-characters and is valid UTF-8.
Fix loading of external sounds in the editor. The wrong path variable was being used, so the sound files would not be loaded from correct folder.
Add tests for new datafile reader/writer functions.
Port map and editor support for `CURVETYPE_BEZIER` from upstream, i.e. support bezier curves with configurable in- and out-tangents for every envelope point.
The in- and out-tangents are represented by triangles and can be dragged in the envelope editor like the envelope points.
Support reading and writing the bezier information as a separate UUID-based map item. If the bezier information is not found, bezier will default to linear behavior. Old clients will still be able to read the new maps and ignore the unknown map item. The unknown curvetype will also be handled as linear by old clients.
Allow reading upstream maps that use `CMapItemEnvelope` version 3. On upstream, a different struct is used to store all envelope points including bezier information, which broke compatibility to old clients.
Fix holding Ctrl for slow envelope point editing not working for vertical movement.
Highlight the currently selected element (envelope point or bezier tangent marker) which is being used with the value/time edit boxes.
Hide the value/time edit boxes when no element is selected.
To reduce duplicate code and to add validation for tile skip everywhere.
Add separate `CMapItemLayerTilemap::TILE_SKIP_MIN_VERSION` constant and change `CMapItemVersion::CURRENT_VERSION` back to the previous version, as maps with tile skip can be loaded but skip is not used when saving.
